“My theory is that Snape didn’t die at the end of the seventh book, based on two points….
1: Snape doesn’t appear when Harry uses the resurrection stone: You’d think Snape was very important to Harry, he loved his mother, gave his life to save him, and shielded him all his life. Harry just found out how Snape had been protecting him the whole time and died to save him, so when he used the magic ring that brings the spirits of dead people, you’d think Snape would be there. He certainly knew Snape longer than Lupin, and you’d think Snape was far more important to him than Lupin, but Snape wasn’t around. Perhaps he was not dead.
2: Snape’s corpse isn’t found or mentioned: After the big battle, they lay out all the bodies, all the people who died, even the death eaters’ and Voldemort’s. Harry sees Lupin’s and Fred’s body, but Snape’s body isn’t there. You’d think Harry would have told everyone about Snape’s sacrifice so they can find his body too. But nope, Snape’s corpse isn’t found.
My theory, based on these two points, is that the snake venom didn’t actually kill Snape, probably just paralysed him or put him in a comatose state.
Just think about it, do you really think a POTIONS MASTER wouldn’t have access to anti-venom? You think he wouldn’t have prepared for the possibility that Voldemort’s snake might turn on him? He was playing a dangerous role as a spy, Voldemort could turn on him at any moment, I think Snape would have obviously taken some kind of prophylactic antidote beforehand.
So Voldemort’s snake didn’t actually kill Snape, it just temporarily paralyzed him and made him look like he was dead. That’s why the elder wand didn’t belong to Voldemort, cause he hadn’t really killed Snape. Snape’s body is not mentioned at all, and his ghost doesn’t appear with Lupin’s and Harry’s parents, even though it should have, so Snape obviously survived.
He probably feels he fulfilled his promise to Dumbledore and Lilly and is out traveling the world and living his own adventures.”
If ever a fan theory deserved its own mic drop, it’s this one…