I really don't think this will happen - Discord has hit a sort of "critical mass" that you don't just kill like it happened with Mixer.

If anything, I hope they will treat it like GitHub and let them act mostly on their own, while actually improving the service.

Recent feature additions point to an Enterprise service they are setting up, so this may be a part of their new strategy while keeping the service accessible to free users despite their crazy operating costs.

It won't. When Google acquired YouTube, there were similar concerns that the platform would be "corporatized" to death and be replaced. Corporatized, it has been, but its dominance in its marketplace is stronger than ever. Twitch has emerged as a serious competitor for games, but YT remains just as big if not bigger than Twitch in this corner.

GitHub and LinkedIn are similarly thriving under Microsoft's wing, without a Twitch-like competitor in sight.

Instagram is more popular than ever since it was acquired by Facebook.

Discord will be fine. Microsoft has a lot of experience in the gaming space thanks to the Xbox ecosystem of services, and in the online chat room space, thanks to Teams.