He had to have known he would be at least a part time setup man. I haven't seen anything indicating he would be a full time closer, and there's no way they would promise that and remove Hendriks from the closer role.
I guess if he was promised he would be a co-closer this would make sense. Not sure the results would have changed much, since he sucked as a setup man and would likely continue sucking as one. It's pretty mind boggling he never got a shot at closing.