I've been wondering for a while.....what exactly is the level of commitment is there for the DB once a contract is accepted? Is it "within reasonable cost/casualities", or does the whole chapter basically have to give their lives trying to kill the target no matter how bad the target is wrecking them?

Are they allowed to say "Okay, we give up" or are they bound by some rule/power to try to complete the assignment?

Considering they keep sending idiots after me, no matter how many I kill, in both Morrowind and Skyrim, i guess it's until the job is done.

but the DB is so skilled that normally never comes into play.