If it is some kind of accident, the pilot, who should be a professional, will completely understand the need for a diversion. If he is insistent on it being an accident and not needing to divert, I would be all the more suspicious and make sure he lands where he is told and is under constant inflight security (fighters right there) and follows a flight plan that approaches NOTHING of significance.
Yep !
Must......there are procedures to prevent dialing in the wrong transponder codes. Every good pilot follows such to prevent such an accidential procedure. Too easy to cross 7200 with 7700 per se.