Hey. Wait for a week I think. Not sure but think he did mentioned how many days he'll be gone.

Well, Pasha disappears because if he's still sitting there being stoned, he's not off buying the gasoline... or fixing up part of the bunker, or any of the things you can pay him to do. I don't recall if this is the case with buying the gasoline, the last thing he tells you is how long it will take him to do the thing.