will some companions be lost forever.

hi, i have a problem. companions like bahestur, first, he said that i can't convince him to stay, so i told him that deserters will be hanged. then, later, he said he will go, and there is no deserter will be hanged option. now, i can't find him, do i have to wait longer or some who left and was told that deserters will be hanged be gone forever?

Well, not sure with SoD but I do know that in Vanilla they'll be available again...eventually.  Took about 8 game months in my vanilla game before a companion that left showed up again.

HOWEVER....if you choose wisely, and tailor your game play appropriately, you'll never have a problem with unhappy companions.

For example, my current set of companions is:
Marnid, Nizar, Katrin, Borcha, Deshavi, Klethi, Bunduk, Artimenner, Jeremus, and Ymira.

Borcha does not like either Deshavi or Klethi (and the feeling is mutual of course).  Artimenner has problems with Jeremus and Klethi.
Borcha likes Marnid, and Deshavi likes Klethi so those 2 likes keep Borcha, Deshavi, and Klethi happy.

Soon though, I'll need to drop Artimenner (name him my regent) or I'll have problems with both him and Jeremus.

There are 2 'rings' of companions that show what combinations are stable, and who will have conflicts.

http://strategywiki.org/wiki/Mount%26Blade/Companions will show you the 2 rings and explain this concept better.

normally its not depending on time but on renown. You have to gain a certain amount of renown (not sure how much) before they reapear