Why would a broken rudder cable cause the rudder to stay fully deflected?
Wouldn't this only affect certain gliders with rudders which are "dual" spring loaded to return to centre position and the one spring breaks?

Faced with the same situation, I doubt I would bail out.
3000 feet AGL isn't very high and there are risks with bailing out. One has no reserve chute should the emergency pilot chute fail to deploy and hitting nasties like power lines on the way down could be fatal.