Realistically, most companies replace their PCs every few years. So there are probably relatively few machines running in offices that don't meet the requirements.
In my experience it is more like every few decades. There's still PCs running XP or even something more ancient. If a company swapped their systems during the whole "W10 is the only OS you'll ever need" period, then they might be fucked.
Obviously depends on the company but well run companies shouldn't have any problems unless they have very specialised machinery but those probably already run Win XP or some shit.
And no company should seriously expect free software support for the end of time.
Eventually when Microsoft will go too far, this is what will happen. Companies already have to do all this training, and given the right OS and IT support there's plenty of Windows like solutions that would be immediately intuitive for people who just browse and use a few specific programs
....but most people are too tech illiterate to even know there's an option outside windows. Hell, I dated a girl who though windows was the operating system on apple devices (she used the term windows and operating system interchangeably)