I believe that it is a common error to assume that if one does not have religious faith, one must conclude that the only thing that can come after death is nothingness and that our consciousness will enter into a kind of void.
The reason for this is quite simple. The argument is that, despite it being true that we might have no evidence about what life after death is like, we have at least two points of evidence about death that we can draw some conclusions from and it is actually the way in which this reveals just how little we know about death that changes the conviction that there is likely to be nothing.
And so, what are these two points of evidence?
I would contend that all of us, whether we are religious or not, can know at least two things about death:
First, we know what it can be like to not be alive (which is the state we were in before we were born) and;
Second, we know what it can be like to not be dead (which is the state that we are in now).
What does this tell us? Well, there are a few interesting conclusions to be drawn from these observations. To begin with, they must apply to everyone who is mortal who had a beginning to their life before which there was apparently nothing as far as their consciousness was concerned. Which, without splitting hairs, means that they are true for everyone.
The next conclusion is that these observations are proof that nothingness does not entail nothingness forever, even if that is what comes straight after death. We know this as a matter of raw experience because we had been in a state of nothingness before birth, out of which conscious experience – i.e. Life as we know it, arose. Therefore, we can conclude from this that if we enter a state of nothingness after death, it is possible that we will enter a state of being "aware" or "alive" again at some point after that.
(This should raise a question about the consistency of identity, but we'll turn to this in due course)
And then we can conclude that nothingness is not even guaranteed if we die because we only have one piece of evidence to go on. The state in which we were in before birth tells us that there can be nothingness if we are not alive in the world as we know it. However, given this single point of evidence we could not regard this as conclusive proof of what happens to life – or at least "consciousness" after it has already occurred because we simply have no evidence for this. Again, all that we can know is that it can entail a state of nothingness, but this does not prove that it will.
Now, this is a good juncture at which to talk about materialism and identity for a moment. After all, one could contend that these arguments do not apply because it is our material being or body that is related to our consciousness and once this dies, our consciousness must end. After all, if our conciseness relies on – say – our brain, and our brain dies, how is consciousness supposed to exist after the fact?
The answer to this rests on recognising just how little we know about consciousness and how it interacts with the body. In philosophy and science there is an issue known as "The Hard Problem of Consciousness" and it recognises that science might simply be unable to tell where the connection between consciousness and the body is. There are "Easy" questions of consciousness such as "is someone awake or not?" or "how much attention are they paying to this or that" these problems relate to the function, dynamics and structure of consciousness and these features can be explained using the methods of science. However, what cannot be explained is the Hard Question which is: "Why is any physical state conscious instead of non-conscious"; where exactly does consciousness arise, how, and how do we know? The general idea is that you could scientifically map a living being down to the atom and not be able to explain why it is conscious, or even prove that it is conscious.
Therefore, there is something ethereal about consciousness that means that it might not be tethered to our physical bodies because we don't know where this tether is. We might be completely non-conscious when the body dies, but there is no conclusive proof of this, unless we can conclude that one's consciousness is ultimately tied to a single body and cannot, for example, move from one body to another. Therefore, it neither goes against logic nor evidence to posit that consciousness could be awake in our bodies now, be turned off or "paused" at the point of death, and awaken again once it emerges in a new body (and I posit this only as one possibility). Therefore, an appeal to scientific materialism does not prove that death is simply "the end" and that there is only nothingness after it.
On a different vein however, there is the connection between our physical bodies and our identity. What I mean by this is that there is a greater case to be made that, even if consciousness caries on or re-emerges in a different body once I die, that consciousness in the new body will not be "me" because all of the things that constitute my identity died with my body. Namely, we can take memory as the main example: who I am is tied up with what I've done and what I can remember about myself. If my memories are stored in the brain, and the brain and consciousness are separated at death, it follows that my identity will not be carried over after death and that even if there is life after death, it will not longer be "me" who is alive at that point. I believe that there are two ways to approach this question. We can either point out that this is not guaranteed, or consider the consequences if we assume that this is how it works.
First of all, we could posit that just as we don't understand how consciousness is tied to physical reality, we don't understand all of the ways in which the contents of consciousness are tied to physical reality, such as our memory. It might be that our memory is stored in the brain, or it might be that there are aspects to memory that are as ethereal as consciousness that are not tied down to the brain. However, even if we could also consider that this possibility may be very slight given the apparent evidence, and it appears more likely that the memories and other aspects of our physical being that make up our identity will not carry over after death, we could still posit that life possibly carries on after death, but with a different identity. In this manner, you or I would have all but our consciousnesses swapped out for new identities at the point of death. In this sense, you or I in the sense of who we are now will die. But our lives as-such might carry on. Consider by analogy how it may be as if consciousnesses is like a series of films being played. Once one film ends, the protagonist, characters and world within that film end, and when the next film begins, its cast and universe come into being. Likewise, it may be as if the film of our life ends and an entirely new story beings, but consciousness carries over and there is still life for "us" in the sense that a film is always playing, whether we remember the one before it or not. In any case, this possibility gives an adventurous spin on the cycle of life and death. If we consider a second analogy, it might be as if the cycle is akin to a series of video games in which the characters from one game do not exist to the characters in the next and as for you and I, instead of having our characters, their memory and the progress of the game carried over from one game to the next, it would be like starting with a new character in a new game each time life renews. Again, I am not advocating that this will actually happen, but positing it as another possibility as evidence that mere nothingness after death is far from guaranteed.
Therefore, the materialist problem of whether there can be life after death can be answered by appealing to the Hard Question of Consciousness and the recognition that there is no guarantee that our consciousness ends with our physical bodies and by pointing out that, even if our given identities end with our physical bodies, there is no proof that our consciousness cannot carry over into new identities.
To conclude then, I have briefly attempted to make a case that we can conclude that there may well be life in the form of conscious awareness after death even if we don't hold religious faith and convictions by appealing to common evidence and logic. The evidence that we all have is that nothingness is a possible state to be in if we are not alive (which is the state before birth), and that we know what it can be like to be alive (which is life as we know it right now). Given that these are the two points of evidence that we have, it logically follows that nothingness is only a possibility after death because there is no contradiction between this and the claim that life can come after death, even if death entails nothingness because it has done so already. Moreover, there is no contradiction between the claims that nothingness came before death and nothingness might not come after because we don't have the evidence that nothingness is guaranteed to occur in death, only that it can. Therefore, it is possible to conclude that there might be a form of life after death without an appeal to religious faith.
Yet, also note that I am not making this argument against religion either. Instead, it is borne out the recognition that many cases that are made for life after death depend upon an appeal to religion. On the merits of this argument alone, it could be the case that any number of religious depictions of the afterlife may turn out to be true, or perhaps something else altogether. That is an open question. However, what I hope has been demonstrated is that, whatever it might turn out to be, we can posit that there may be life after death, and we can do this through an appeal to common reason.