If you believe your a good coach, and there are no HC jobs open, I don't know why you wouldn't take a job for a team that has a lame duck coach.
Not only do you end up with an inside track for your current teams job, but if your units played well despite the HC not doing a good job, that looks good as far as being able to succeed in less than favorable situation.
This is the NFL and not college. I don't think the HC situation matters all that much to other coaches or players. There are only so many open slots, unlike CFB, so you take them when one is offered / open.
JMHO