I'm guessing a bit. If you have the computer set up to log into the Microsoft account, then Office 365 will use that login. If it isn't set up that way, then you should still be able to connect to the Microsoft account through Office 365. I believe that is a one time authorization. I've set up computers to log into my Microsoft Onedrive account that way, but never tried it with Office 365.

Personally, I'd set up the computer with a Microsoft account and secure password that you have memorized and/or recorded somewhere (Microsoft can help you recover that password if necessary since there is an email address tied to each account). Then I would set up a simple PIN code for each computer and have that taped to the screen, in a drawer, or something. Takes 2 seconds to type in a four digit code if you pick a simple pattern. Code can be longer if you decide to enhance security in the future.

When the computer gets stolen, all you have to do is log into its Microsoft account from any web browser. Disable the computer from the account and any on-line data is secure.