China, Laos, Cambodia and Thailand don't normally use the carnet. (Some people had theirs stamped anyway, but that's a different story.) None of them stamp anything about your car into your passport, so leaving without the vehicle is not a problem. Been there, done that.
So, you could try to enter Thailand as suggested, meaning you won't have a temp. import permit. You could then try to sell the car (for parts, maybe, if it's a model common enough there).
You can also legally leave the car with customs, i.e. donating it to them as a write-off. Even with a carnet this should be possible, as long as they stamp it out.
You can also drive into Malaysia without any paperwork, using one of the smaller border crossings. (Done that.) You could then either sell it for parts or abandon it.
Better still, there are lots of Burmese refugees eeking out a living in Thailand. Leave it with them. They even recycled my old helmet that I left by a rubbish bin.
Yes, China can be done, if you are prepared to spend the money and take the guide with you. Expect two months lead time for a tour co. to organise it.