Strangely, Teams chat is working fine here. Anything in Teams that is tied to other parts of O365, including the calendar, is dead. I'm currently watching a training video on sharepoint.com, so that's fine too, for now.
While I don't expect this to be the case, I'm emotionally prepared for this to be some sort of "dicks out for Harambe"-style action protesting JH's departure from Nvidia, on a larger and more technical scale.
Edit: Typo.