AU I will probably never write: the clone wars happen earlier than in canon, making Anakin a padawan for its whole duration. When Palpatine starts Order 66, Obi-Wan is still alone on Utapau, having left his sulking 19-year-old padawan back at the Temple as a mild punishment after another display of bad temper and rash decisions.

He then spends the next few years of his life alone in hiding, thinking that his decision killed his dear padawan and that their last words to each other were sharp and bitter.