I don’t think anyone can make any guarantees at this point.
Microsoft doesn’t do Mac games, but there’s no indication they’re overhauling the development department in Activision-Blizzard either. Everything published so far indicates AB will become a wholly-owned subsidiary, not chipped up and distributed throughout the rest of Microsoft Games, which means they would still have their Mac development teams.
But there’s no being sure it can continue that way.
I don’t personally recall, but does anyone else remember how other Microsoft Games acquisitions fared? Did they keep their development and product lines intact?