Just my 2 cents here since everyone is legitimately freaking out over very minimal changes.
Sega Sammy as a corporation had a bad quarter. They are restructuring the business for better efficiency and to make sure that their entertainment business works in tandem with their other divisions better. This includes Sega's game publishing and development arms. This doesn't mean they are "about to get acquired".
Sega is part of Sega Sammy Holdings which is a public organization. It doesn't matter if it's in Japan or not, by law, they are required to announce to their shareholders if any acquisition talks are happening. The whole Japanese company angle is so that the country doesn't lose significant tech companies out to outside investors. Here's a link.
That doesn't mean any acquisition
won't happen, but Resetera has a lot of clout, and this freaking out over a business restructuring its divisions thinking it's an acquisition should definitely trigger their PR and internal team to put out statements to calm the fire it really goes out of hand. They could definitely sell off their entertainment arm, who knows but that's not the reason for the restructuring that's happening.
Finally, yes, this would be a decent move for Microsoft to cover their Japanese games gap. Sega currently publishes and develops a lot of niche games, and them being available on Game Pass would be a big boon for their catalog. However, people who are excited by "OLD SEGA IS COMING BACK" need to relax. Sega currently has several projects in development, not to mention games to publish and Atlus to support. They won't magically be able to bring you back to the 90s out of the blue. If an acquisition does happen, we won't be seeing any "new vision" of Sega for at least 3-5 years until the company gets slowly consolidated into Xbox Games Studio. Even if they stay at a low integration model like say Mojang or potentially Bethesda, they can't just cancel everything and go back to pleasing the 90s kids. Just take a look at Rare. We get a few nods to nostalgia every few years, but generally speaking, they are focused on creating new content.
I know people are excited, but this isn't doom/gloom or amazing out of the blue. If it happens, we will surely know about it before everything is approved.