Patchy is like Voldemorte. That's why he can't die. The secret is in the horcruxes. Mikhail ripped out pieces of his soul, like Voldermorte, to keep him from ever dying. The eye that the Tailies found in that Bible in the Arrow station -- that was one of Mikhail's horcruxes.
Clever. I like it.
(but that doesn't mean it isn't stupid)