I don't know what happens, I don't really think the Heaven/Hell thing happens, but subjectively speaking there can't be nothing. Right at this moment you are conscious, therefore you are not unconscious. Can you describe what it's like to be unconscious? No, because if you are unconscious you fail to perceive, and a description is a representation of a perception. You can't be conscious of being unconscious, which is kind of a self proving statement. In the same way, an area of space cannot be dark and light at the same time, because darkness is the absence of light. It can be less light, but there still exists light, and not darkness. There cannot be nothing after death, because you would need a method to perceive that nothing. That's too easy an answer. There has to be something after death, but it isn't nothing. If there were some nothing for you, there would eventually have to be something, and because you can't perceive that nothing, then time would pass instantaneously, because you would not be conscious of the time passing. From your own perspective, life is never ending. It seems like life ends for other people, but that's just because we don't perceive what they do. So, perhaps, you could die and then simply fail to perceive time moving backward and live your life over again for all of eternity. That's a more sensible argument than nothing at all happening.
Observing nothing is impossible. Even if you found an area in space where there are zero particles in there, and is completely shielded from the background radiation of the universe, it is still a space. It is still volume that is measurable, which contradicts the real meaning of nothing.
Humans are limited in the fact that we cannot perceive infinity. Nothing is kind of like infinity in that regards. Just because we cannot understand it doesn't mean it doesn't exist, just the same as just because we cannot see a 4th dimension doesn't mean it necessarily doesn't exist.
Nothing is really just the absence of perception, I suppose. Something is a known quality or quantity--a perception-- so nothing is the unknown, essentially. If we can't know it, we can't perceive it. If we can't perceive it, it is nothing. Not until we perceive something can we truly believe it exists.
Even trying to perceive nothing is creating something. I think it's possible that there is nothing after death because death could just be the ending of consciousness and perception. If we're truly dead, we couldn't perceive and so thus there is nothing. No thoughts, emotions or anything. Its not a sad, dismal concept if you think about it. You wouldn't be able to regret death or be sad.