Disclaimer I don't own Harry Potter.
The boy and his two annoying insufferable sidekicks had just left Snape between in the boat house just a few minutes ago. Once he was sure they were gone, he opened up his eyes and began fixes his wounds. He didn't plan for things to play out this way. He was original just going to disappear after giving the boy his memory. But this works out far more better, because he had eye witnesses to his 'death'. Given his life and his role, he can't just disappear because they will find him unless they think he is already dead.
He transfigured a nearby rock into a lifelike version of himself, incase someone came to collected the body.
He watched from far, watching the battle play out and Harry finally putting a end to the Dark Lord.
Once everything was set and done, Severus apparated away from the school. He was shocked that he was still able to apparated on school grounds, he assumed that the school was still accepting him as the Headmaster and allowed this final request.
Thousand miles way from the school as well as London is where Severus travelled to, the trip took about dozen apparations to make. This fresh started, he wanted nothing more then to be far far away from anyone he had ever know. He wanted nothing more then to be away from all of it, he was no longer needed there. The school had no longer any meaning for him anymore and it was just a place that holds nothing but painful memories.
He was now in a small removed village near the Rocky Mountains, he was surrounded by trees and a small lake. Nearby the lake was a small house, which was privately owned by Severus. For the rest of his days he stayed there. With his only contact with other people will be when he walks to the local village for food and other supplies, other then that he had no contact with anyone. To everyone in village he was just a mysterious odd looking man, he left them alone so they left him alone. Severus Snape is believed to be dead, and he wants the world to believe that he is dead. He wants nothing then just life out the rest of life his alone and in peace.