I wish I could agree with this, but the ecosystem lock-in is too great. They might lose business for sure but it may not put a dent in their revenue at all.

If you replace office, you'll have to replace sharepoint, onedrive, etc.. and it isn't just the tools but the policies and critical features that go along with those. For most orgs, this is literally their lifeblood, not just some tool they can yank out. For smaller orgs it might be easier, but those don't pay Microsoft as much anyways.

From a user point of view, there are tools that have similar features, some even better features. G-suite is the only platform i know of that unifies all the office productivity products like 365 does. But neither G-suite nor any other platform can be managed/policed as well as 365. At the end of the day, will Google behave any better than Microsoft anyways (cost or otherwise)? And it isn't just policing and management but securing all that precious data in there, Microsoft might not be great but lots of tech-debt has gone into securing it within that platform. A migration would be costly, justifying it with cost savings alone might be difficult.