I have already @adara-io disabled Azure AD sync, as I've read it can take a few days to really stop. I have also deleted all of the synced users out. I understand we'll have to re-create the Outlook profiles, I'm planning to get ahead of this with distributing instructions for users. Still expecting absolute chaos though.
It looks like with Minimal Hybrid only works if you don't continue to sync AD, which we would need to, so I don't think that's a viable option.