Losing your position from being wounded and losing it from being imprisoned happen in different ways. If you are imprisoned, you will either lose your title immediately or not at all. If you are wounded, then it takes time to lose your title. You have to be wounded over a certain level for a certain number of days. Then you have a chance to lose it after that number of days. (I don't remember the number of days.)
I think it may still be possible, though, to instantly lose a lordship from an infiltrator attack, if you hit hard enough. Not sure...
