While I doubt that Fisher would get fired after 2 or even 3 bad games to start the season, if it were to happen, I imagine GW would take over since he does have Head Coaching experience.
I personally think that Fisher should be fired immediately. He's run his course, and he is who he is.
It's not that I think that the Rams will necessarily even be that much better this season with a different HC (who is bound to come from his current staff), because at this point the offense and defense and players are set for the season. But the differences might come in aggressiveness, boldness, attitude, and very likely we'd see Goff start to get his feet wet because the year is highly unlikely to produce much else than some player development.
An early firing would give college and Pro coaches a heads up that there will be an opening in LA, and Kroenke and Demoff can get an early jump on the process of making a HC candidate list and then winnowing it down, and be ready to pull the trigger immediately once the regular season is over.
I'd love to see Jimbo Fisher at or near the top of the list. Great college HC who wins Championships, and coaches a Pro system.
Wouldn't even mind seeing Norv Turner as a mention, and I'd be ecstatic to see Martz involved somewhere (maybe as OC), but I get this feeling that he is a pariah around the league for some unspoken reason.
What we need is an HC that is either offensive minded, or who values scoring points and would bring in a great developer of QBs and offensive systems. To me, Martz especially fits that bill. But, Norv has developed some darn good QBs too.