Re: I... only supply O365 because my clients have asked for it.
As someone who has worked in environments where "Stay until it is fixed" is the expectation, I am not comfortable with acceding to such requests, even with my advice set out in writing. The risk analysis does not stack up favourably. I prefer to be in control of a situation such that I can sleep at night.
One argument I have heard a lot of is that "If O365 goes down then everyone else is in the same boat." Whatever happened to the USP that "we have resilience where other's fail"?
Incidentally, if I am not mistaken O365 in decimal is 245.