Bent rim and mangled spokes.

I would just upgrade the wheel to a heavier duty wheel. To me when something breaks then it's time to upgrade to a better part.

how did it do an uncontrolled burnout with no carb?

Well at least you seem to be okay. Bikes are replaceable and limbs aren't. I'd get an upgraded rear rim, because more strength isn't a bad thing. Then possibly think about getting a spring loaded tensioner or deleting it altogether? Just my opinion

sry to hear abt ur problem.
do what mota says.
and pin that tensioner so it can not rotate!
best
rc

I would upgrade the spokes and strengthen/remove the chain tensioner. It happened to me once; chain tensioner failed and destroyed most of the drive side spokes. Unless your rim was a single wall alloy, the strength of a wheel comes from its spokes and how it was built. If you want to continue using the rag joint (which works fine with the small engine) I would just upgrade the spokes to 12g or 13g and use a double-wall aluminum rim such as an alex dm24. The most important thing in wheel building is properly stress-relieving the spokes. If you've never built a wheel but want the least hassle now and while riding, I suggest you have a professional build and stress relieve the wheel for you. A wheel with a crappy rim built and relieved properly will be stronger than one with a HD rim built improperly.

Also, you need to use blue or even red loctite along with lock washes or lock nuts on everything. Over time because of vibration, things that are not properly mounted or are just plain weak will break and fall off. This isn't your regular heavy duty bicycle. This is a motorbike-- you need to build with vibration in mind.