The UK blocking the merger doesn’t necessarily stop it. It could be overturned on appeal or the deal could be modified to suit the UK’s concerns.

It’s also theoretically possible that the deal goes through despite the CMA not approving it. I’m not a lawyer and I don’t know if that looks like Microsoft no longer selling games and gaming in the UK (possible) or no longer doing business in the UK entirely (not likely).

Besides, the US filed suit back in 2022.