You take it way too far in your mind. Blocking the deal has nothing to do with banning MS. MS will be 100% fine doing what they always do, and no one will even get to start thinking banning MS. They didn't do anything wrong here, and if it's decided that the merger will not be going through it won't go through. MS will go on with their business as usual, CMA will go on with their business as usual, Europe or whatever other countries will go on with their business as usual.
It might be crap for the Xbox brand itself though, not securing more exclusives which aren't exclusives (rolls eyes). It's quite funny it's all about COD as well, like, what about all the other Activision/Blizzard games staying under the radar? What about Diablo 4, what about their other games? Will they remain available for other consoles? I think not, and we all know this already, so it's not strange to think/know that MS somewhere in the near future will make their primary COD product exclusive as well.