The docs don't say whether the result of GetCurrentThread() is a valid argument to TerminateThread(), iow: whether a thread can cancel itself.
Can it? And if yes, does TerminateThread() then return at all?
Yes, TerminateThread can terminate the current thread. The result of GetCurrentThread has THREAD_ALL_ACCESS rights, so that handle can be used too.
No, TerminateThread won't return in this case.
No, there is no reason to ever do this! Don't.