Thanks ALLFOUR_Rich for the feedback. I'm not sure I have ever seen any hostility from the Exchange team on this subject, if you have specific examples I'd be interested to hear them.
We're sorry the situation isn't as easy as it should be. We really are working on figuring out the right way to allow you to remove the last Exchange Server once all the mailboxes have been moved to the cloud - and that's ultimately the answer to this. Once we have that delivered you won't need to worry about any of this. If a customer then wants to keep Exchange on-prem for other reasons, they can, and that will require a license.
We really do want to allow customers who have moved to the cloud to remove that last server, it's just not that easy given the way the product is architected.