Fortunately, I caught it before it hit the collapse point. Dumb luck, I have to say -- if it'd gone another six hours, it probably *would* have collapsed, and that would have caused significantly more hassle and damage. By relieving the pressure now, I *think* I've limited the damage to just replacing the drywall.

(And yesterday appears to have been warm enough to relieve the ice dam problem, at least for now -- it doesn't seem to be dripping any more...)