You flashed through the important parts pretty fast in your video, so hard to assess the damage to the cylinder? If the cylinder walls are not scored by the debris then you should be able to use it. Same for the piston really, if it's not disfigured from the debris and still has both pins in place in the ring slots that set the ring position you may be able to just install new rings and run it. If any/all of the able parts have been damaged then you need to replace them. Another worry is you might have some debris down in the bottom end that could resurface after the rebuild and take out the top end again, so it would be good if you can piece together as much of the rings as possible to get an idea how much is missing? I've heard people say they flushed out their bottom ends with gas to try and get debris to flow out of there (never done it myself). Also, what about the condition of the needle bearing in the connecting rod?
I really see no reason this motor shouldn't run again. If you do repair it, take some good advise and replace all the studs and nuts with better hardware, if you don't want to source them yourself SickBikeParts.com sells nice hardware kits pretty cheap. Good luck...
