I'd rather see him stick around but would understand the move from a personal and family standpoint. For a guy in his health it would be like a semi retirement. He's had a rough year with the gall bladder operation and the knee getting wrecked before camp. In the introductory presser with Weiss, Haley, Crennel, and Emmitt Thomas, Romeo joked that the coaches needed to lose weight like the players did in the first year when Haley and Pioli came in.
I could see Weis taking Bernie Parmalee with him to be in line to replace him when he does retire or atleast be in position to if the cards fell that way. Parmalee moved up to the booth early on as he was on the sidelines. Might not be much involved there. I just remember pre season he was actually helping Hoffman coach ST's and doing opening kick huddle breakdowns and then sitting in the booth next to weis.
So if true i'd say its a combo of his health and wanting to coach under less stressful situation during the end of his career. The timing sucks but they always do in these situations with playoff teams.
Big credit to Weis for Cassel's development. With the players both new and the strides some have made plus hopefully additional help on the way next year i don't see too much reason to lose hope. With Cassel Haley is going to want to make it as painless as possible. I don't see a promotion from within.
Greg Oleson the oc of the Bucs could be available and Haley has had interest in him before as they worked together in Chicago. There was some article out i don't know where now that said the GM and entire coaching staff and front office all have expiring contracts after this season and don't know their futures as the Glazers are waiting on CBA talks. So just a maybe for Oleson but IMO he would be high on Haley's wish list. Tampa fired Jeff Jagodinzski within days/a week or so after Gailey got canned in fear KC would ask permission to hire him even though the season was close and it would be a rare situation. On the other hand Jagodinszki was fired to because his apparent ineptness as an OC and the only thing he seemed to be able to do was install a zone blocking scheme for the OL. Oleson was already doing most of the work as QB coach.
Rob Chudzinksi was with Romeo in Cleveland as OC and now back in SD as Asst hc and TE's. Jeff Davidson the Panthers OC is another Weis pupil and will likely be available as John Fox's contract runs out after the season and it would be very safe to assume so does davidsons. No really direct connection to haley with those two just from Weis and running similar offenses.
Throw Brian Daboll the Browns OC in that mix as Mangini has a good chance of getting canned next week and holmgren won't need a Weis/Pats former QB coach in Daboll. He has made clear before this season that he let them run their offense and it isn't anything to do with the west coast offense he runs.
I don't see Grimm as a possibillity. He is more from the Cowher tree and could possibly be the next Panthers HC if Cowher doesn't take the job.
McDaniels would be great for Cassel but i would be worried about Josh's reputation since getting a HC job running people off and generally doesn't seem to be liked and how good of a fit he would be in that way. If that's what they do i'm sure it would be clear cut and hatchet burried as any major risk would be a stupid choice for a guy like Haley in his situation being on such an upswing if he couldn't trust or get along or distrupt cohesion of the staff by adding a guy like that. On the other hand maybe getting fired has humbled McDipshit who knows? Damn i sure liked teasing that pony riding piss ant.

Now i may have to pull for him next season. Such is life in the NFL i guess.
It wouldn't suprise me though in the least to see Haley just go with a system guy, like minded and experienced in the offense with one of the others listed and not McD. With Romeo, Haley can still heavily influence like he still does i assume and not worry about having to control a guy like McD if they just aren't a match.
I could see Sirriani promoted to QB coach as that is basically part of his duties now. He is a Haley hand picked youngster and I think he slowly wants to groom him to possibly be OC someday.
The timing of all of this sure does suck though.