Nah, if the acquisition is blocked (something I highly doubt) they'll simply try to buy someone else like EA or Take 2 and some other big mobile gaming company. And won't sell Xbox.
I think that they'll stop making their own consoles and will complete their Sega-like transition to becoming full multiplatform 3rd party publishers on consoles (while keeping their digital store in PC and if allowed in mobile), and wil stop giving away their games day one on GP.
But not today, several years in the future. Because they invested several billions on the acquisitions and the dumb 'all our games and a few AAA more day one on GP' idea, so they'll wait at least 5 years to see if it works even if they always knew it won't.
MS is not on sale even if the deal fail and nobody has interest in buy Xbox.
Yeah, nobody would buy it and I highly doubt they ever consider to sell now the division.
But if some day MS does it, if not overpriced Tencent would be interested on buying a few dev studios and IPs, Sony other ones, same with EA, Take 2, Embracer, etc.
But nobody would want to buy the Xbox brand itself and the console. If Apple, Tencent, Samsung etc some day want to have a console they'll create a new one.