Yeah, I think the only way to know is if you tried to put it in gear. If it just locked up on him, my guess would be something in the tranny broke (i.e. a gear or something, a shift fork shouldnt have broken if he wasnt shifting) and is preventing it from turning. If so, a tranny rebuild is in order but your quiaffe should be ok provided it didnt get shit all up in it. I would just try it while its in neutral and see if it can shift, then be gentle and try it running. If theres a gear broken, you'll know it.