Look, McDaniels is under contract and the Rams will not let him go "just because" now if they hire Fischer, I'm sure that he is going to let McDaniels go, but he might be owed money by St. Louis if that happens. On the other hand if they allow him to leave to another team, I'm sure the Rams would be off the hook for any money owed to McDaniels.
Bringing him back is a no brainer. Let him reestablish his HC creditials, give BB someone he trusts to take over for O'Brien. What will be interesting to see is when the Rams release him, how quickly he returns to NE, does he return for the playoffs?
The best case scenario is the Rams hire Fischer (keeping him away from the Phins, becuase he is a very good HC), then KC makes a mistake and hires someone not named Romeo to be their next HC, Romeo comes back to NE to be the D coordinator, McDaniels is the OC, and away we go...............