My guess is that something came loose (like the the pinion nut):-) and that if not driven any more may be able to be saved.
It's going to take some pictures and some specific answers of findings to get to the bottom of it quickly.
Does the driveline move up and down or sideways at all with no load on it? (like the parking brake on with the car in neutral)
Second question: Does the the whole yoke move including the shaft behind the yoke where it goes into the rear end?
Do both these at the rear of the driveline, so just grab it yank around on it a bit and report back.