Yeah I dunno. I feel like we know exactly what happens, as others have said. To tediously spell out the obvious case again: you're an organism, what you think of as "you", your consciousness, is an illusion brought about by various physical processes in your body, particularly in your brain. When you die those things cease, and so do "you". I don't think there's much real debate about those things. Of course some people feel differently, but those people have been established to be incorrect, in my mind. Anyway even if you did believe your consciousness survived death, your body clearly doesn't. Ask someone who works in a morgue what happens to bodies after death, it's nothing transcendental. You don't have to accept the prior that your consciousness is part of a physical process really.
I think people have a moral obligation to help others as much as they can, at least when it doesn't inconvenience them too much. You wouldn't let a small child drown in a shallow pool of water, because it's well within your power to save them and costs you very little. Similarly I think you should let other people use your organs when you die. They do you no good and they could help someone else. This isn't going full anti-spiritual and saying you should eat your grandma when she dies because she's just meat, or whatever. And it's not saying you must sacrifice everything to help others either, just that if you can, easily, for little cost, and you don't, you deserve moral judgement.