In the case of D:OS, terminating your Steam Account, you can still play the game.
(Or so I've been told, haven't tried it.)
I do know you don't have to have steam running at all to play D:OS.
You would think but the Steam terms say otherwise outside of the EU. The latter half of this article covers this well with input from an actual legal professional:
Basically as of right now outside of EU Steam is overriding the publisher on license termination. It can get away with this for now until a legal challenge occurs.
