In the specification/doc of std.thread:
void wait();
Wait for this thread to terminate. Throws ThreadError if the thread hasn't begun yet or has already terminated or is called on itself.
The implementation does throw an exception if called on itself: OK
The implementation does throw an exception if pthread_join does not succeed: OK
But throwing an exception if the thread is allready terminated not implemented nor would this be useful - you cannot check that the thread is running and be sure that until calling the .wait, the thread does not terminate.
So, like it is implemented, wait should return without exception if the thread is terminated.