Okay, here's one.

you can usually have one of three DB followers. I believe, if one dies in your service, you still can't enlist another one until the dead one respawns (?)

I took the khajiit db follower with me on defense of bruma. well, of course he died on the battlefield. He did NOT follow me into the oblivion gate.

It has been many game weeks since his death. I even finished the MQ line now. But he has not respawned in the sanctuary and i can enlist the other db followers freely.

Is he gone forever? I suspect there is a glitch with the defense of bruma scripts, as at the end of the quest, not all the bodies are still on the field. That means there must be some script that deletes some of the bodies for some reason. If the db follower was deleted in this way, maybe he is gone forever?

If that's true, it's something ppl should be aware of.

If one of them should die, then they will respawn next to you in one week, assuming you haven't chosen another one to follow you. (http://www.uesp.net/wiki/Oblivion:Dark_Brotherhood_Murderer)