Yes back to the original question.

A while back there was a thread named "Understanding a Sally" I think, dealing with how your inferior garission could wear down their enemies in sallies and eventually defeat them. I think the original poster here would reap much benefit from reading that thread. Even if vastly ouynumbered there is no reason to just wait, starve, then fight to the last. You can do some serious damage to the besiegers in sallies.

Now when I actually met this thread first the poster had already fought to the last and inflivted heavy casualties. But for the future the sally tactic may be beneficial. Or if he has a savegame he can go back and try again.