I have completed migrating user mailboxes to 365. The only mailboxes that remain on-premise are system/service mailboxes that don't use mail clients (and as such don't need Autodiscover) that won't or can't be migrated to 365.
So my question is this: When I remove/change the Autodiscover information, what will happen to clients (both internal/external Outlook clients as well as mobile clients)? For example when mailboxes were migrated users had to remove/re-add their mail account on their mobile devices. Will that need to be done again when autodiscover is removed? I really don't want to go through that again for almost 1000 users.
Also, what are the best steps for doing this? I understand I should set the AutoDiscoverServiceInternalUri to $null on the Exchange server (which I'll be keeping and in hybrid mode), and publish Microsoft's autodiscover information in my DNS, but is there anything else I need to be aware of?