Mafia 106. Plague. Dragon Utopia

What will he do if he's the only one left on the team and the killer somehow disappears?

If only Shabnak survives from the negative side, the town wins. Unless, of course, he's only left in the form of the Impostor.

Does it protect against execution?

No.

And what will he do against the killer himself if he's the only one left on the team?

He'll try to execute him during the day and infect the town at night. Although this situation is very bad for the Mafia, if they allowed the loss of the Prophet and the Albino, they deserve it.