So after killing my 19th Dark Brotherhood Assassin or so in Skyrim, a thought occurred to me: exactly how bound is the DB to completing a contract once it is issued/accepted?

Like, do they have to complete the contract, even if that single kill means they'll lose the entire organization? Or is there a point where they're allowed to go "Ok, this is getting out of hand, I think we should give up on this one."

Because its not like its impossible that one day they might get a contract on someone whose taken so many levels of badass that the DB really doesn't stand a chance of killing them through any means - are they really required to through themselves away on this person, or can they be give up or deny it and live to see the next day?

Its bad business to refuse contracts. Its even worse business to accept contracts you can't complete.

Of course, that would be the Daggerfall Dark Brotherhood's answer. The newer asshats probably just through bodies at stuff until it dies. FORR SITIS!!/3/34!34/!

To be fair, the Dark Brotherhood in Skyrim only sends one assassin for each time they are called, failing is fine for them. In Morrowind they were not that big a bunch of Sithis worshippers or at least they did not appear to be so, and they still send assassin after assassin after you, until of course you wipe them all out.