I've had two of your scenarios happen to me, the TO bearing slipping off the pressure plate and the clutch fork breaking. They felt different to me before it happened.
When my TO bearing let go it was sudden, like you describe. The only warning I had was a bit of clutch shudder on takeoff in 1st. This was because it was beginning to let go on one side first so the pull wasn't even.
When my clutch fork cracked I found it would take more and more pedal to get the clutch to release. I thought maybe my cable was stretching so I adjusted the cable. It was better for about two days and then happened again. Not a sudden failure.
My money is on the TO bearing breaking or slipping out. Sounds like you have no choice but to separate the engine and tranny. Opportunity to replace clutch parts I guess. Rebuild the tranny maybe? I mean... while you're in there
