I mean if there's an afterlife or anything.
I think what I'd most like to happen is to be able to go back through my life but from other people's perspectives so I could find out what other people were thinking during times when I wasn't sure how they felt, and find out what went on in their lives when I wasn't around and how that impacted on their interactions with me so I'd be able to see the bigger picture and where I fitted into it.
What I'd most hate to happen is to find out God exists and to ask him if there's a Heaven only for him to say "What do you mean, is there a Heaven? That was Heaven. I put you on a planet with attractive women, illicit substances and a society with loose morals. Why the hell didn't you make more of it?"