Is it possible to completely destroy a faction in Warband? In my current game the Swadians and Vaegirs have lost all their holdings since ages. Their last armies are still around, and even if they are destroyed they reappear a little bit later. They are especially annoying as they are both currently at war with my king and keep on raiding villages if you don't hunt them down over and over again.
You are sure that they don't have a remote castle somewhere you've overlooked somehow? You should be able to be absolutely sure if you've checked the faction notes and they have nothing under holdings. If this is the case only thing I can think of is that their lords can use neutrals castles and cities to hide out and rebuild their forces. But their lords should not respawn if their faction has no castles. If they have no holdings and you've encountered and completely destroyed the forces of one of their lords more than once I'd say it sounds like a bug.
What patch are folks playing on in this thread? 1.151+ has been attempting to fix faction defeat problems introduced with lord respawn changes that were made in 1.143. So, in order to be sure folks are talking about the same possible problems/hangups, the version is very important.