If you're "lucky", you might have fragged the clutch basket and/or plates. Common problem (so I'm told) is for the fragments to get tossed into the kick start gear and bind things up. Drain the oil, pull the right side cover off and see what the clutch looks like. If it's fragged, you'll need to pull the right side case cover off and clean out the millions of tiny (and not so tiny) particles that have scattered themselves into the backside of the case cover. Taking this case cover off is easy, btw. Remove the rear brake pedal, and take the oil line loose (one 8mm head bolt). Then take the 8 or so bolts off holding the case cover on. You should drain the coolant first, too. Drain bolt is on the water pump cover, which is mounted to the front of that case cover.
Same thing happened to Thunder33's bike a little over a year ago. I thought for sure the small end of the conrod had let go, which I have also seen happen. Turns out the clutch basket just let go. His gave a little more warning though, it was making some not-so-good noises after riding around for a while. He made about 1/4 lap or less after that, and it was locked solid, but would still roll in neutral.