I wouldn't say they'd never do an Office on Linux... If you look at how they've been leveraging web tech and Electron for VS Code and MS Teams, I'd be very surprised if we didn't see an Electron based version of Office in a couple years. Electron has an amazing cross platform appeal for developers and MS has taken advantage of that. Not to mention managing to write applications under Electron that don't suck (though memory usage is high).
And despite high memory usage, Office has never been that nimble in terms of ram use anyway.
As for AD, Azure's hosted services for this may well see more inroads into Linux, and I know a LOT of people/companies that would be beyond happy to use MS account management with a cleaner Linux integration.
I won't be using these things at home any time soon, but in a corporate space, MS would be a welcome and cost saving change compared to what is out there on Linux currently.