Good point - that is, if he can catch the true thread with the tap. If he catches the crossed thread, then (as the Dead Kennedys say) you've got a "bigger problem now".
There are also these very clever thread chasing tools, that compress and fit into the threaded hole, allowing you to get past the damages portion. You then tighten the tool, and it expands into the good threads. Then, you back it out and it chases the bad threads as it comes out of the hole.