Nope none of that has to happen just as Ancelotti didn't have to change to diamond and sacrifice a winger to try Jude at 10 and bring players in from the wings tighter.
Plenty reasons to think he'll change formation to suit squad with more wingers benefitting from more minutes including Ancelotti own words he prefers to adapt to what's at disposal
Bellingham can play deeper without much an issue as proven at Dortmund. Whether or not it'll work in RM is a test we're likely to see very soon
I bet you didn't watch much Dortmund. He was decent deeper, but not more than that.
There is a huge difference between what he offers as a shadow free-roaming striker that he plays for Madrid and what he can offer as a CM.
Ancelotti will surely change formation if there is a reason or objective for it.
If you remember correctly he used to play with 4 mds (including Valverde) in all important games in 22/23 season. Belligham's arrival necessitated an amend in formation, and if Benzema had never left, he would be playing the same diamond with Benzema instead of Rodrygo
Now Mbape's arrival doesn't necessitate anything more than benching Rodrygo.
Besides, this free style of the three upfront w/o fixed positions might benefit Mbape
I bet that will be his formation and system for all the big games, and if he tries something else he will soon revert to this