Office 365 might be a great idea but the actual execution isn’t ready and you’d need your head looking at if you put your faith in a Microsoft to run your business systems.
Your experience might vary but that doesn’t make my point of view any less valid.
Have to say we've had the opposite experience at work with O365 which kind of surprised me as these days I've very little faith in MS to execute well. Aside from the odd account issue like you mentioned (we just created another account and AFAIK the original ones are still ***** even today and I don't believe there has been any problems with actively used accounts) which is quite bizarre to my knowledge there hasn't been any downtime or missing data, etc.
I think the account problem is down to some kind of truncation somewhere of the username or similar which really should have been ironed out by now.
Personally though I think there has become a bit of an over-reliance on cloud platforms for day to day operation without enough fallback - its been a bit of luck that there hasn't been serious service disruption so far.