Re: Possibly even a good one.
I'd tend to agree on PowerPoint, but that's not the point.
If my employer had it's 365 turned off, then we'd be ... well and truly fooked. No email, no access to any of our documents, basically f'all ability to do anything. Yes, there's some secure non-MS communications channels so the front lines could still get basic instructions, but I think it would be easier (by orders of magnitude) to list what could still be done than to list what would stop working.
No comms - it's all Teams and we got rid of phones on desks.
No email - it's all Outlook and Exchange
No access to documents - I shouldn't need to elaborate on that
No browser - Edge, and on some systems Chrome is gone
No access to internal web sites anyway - that's all Sharepoint and similar horrors
And none of that would matter anyway, because we couldn't log into our computers in the first place.
I imagine commercial negotiations are basically : MS says how much they want us to pay, we ... agree to pay it. We have no bargaining power because MS knows that we could not leave without a multi-year program, massive upheaval, re-engineer most business workflows, and so on. All they will do is offer a bit of a discount to take the edge off and make it look even worse to leave.