Personally, I'm against bringing in a new coach like Mitchell/Cheeks. I just want someone like Natt or Person to be promoted, so they can get the chance to try something new with the set of players we have. Sometimes, a team just needs a new voice in the locker room. For all you 49er fans out there (sorry to change sports), look what Singletary has done so far this year since he took over. He took the same players, the same system (but obviously adjusted it), and made it better.
So, go with Natt or Person for the rest of the year, see how they do, if it doesn't work out, then interview for a new coach in the offseason *COUGH* Tom Thibodeau PLEASE! *COUGH* and go from there.