It's still repugnant to me, as compared to self-hosting, but I would never self-host for a greenfield SMB Customer today. The economics don't make sense and the talent pool of knowledgeable and reasonable sysadmins is dwindling by the day. (I wouldn't want to make a Customer so beholden to me if they were willing to pay for it.)
I miss being able to spin-up an on-prem email server on a box with reasonable hardware redundancy, some external USB disks to rotate for off-site backup, a UPS, a couple consumer-grade "business class" Internet connections, and a contracted "backup MX" to catch email in the event of an outage. It was a good enough for a lot of small SMBs who had a physical office, and was cheap.
The difference is that everyone's account kept working during that time so business kept on as usual, just the admins couldn't change anything.
The sad thing is I don't think anyone did anything unusual and it was some kind of bug of Microsoft's end.
Moving the MX for the domain and limping along from backups is my worst-case contingency but given that there's no place other than M365 to restore the backups to it isn't a very good strategy.
