1) Keep Office Windows (and Mac) only as some sort of "competitive advantage"
2) Expand Office to iOS and Android, too, which will have billions of users in the future, more than the Windows ecosystem itself
3) Keep prices as high as ever
4) Dramatically lower prices by an order of magnitude to make sense for the mobile ecosystems, and be more competitive with free or sub $10 Office Suites, that while may not have all the Office features, it will have a lot for many people. If they didn't think that was true, they would've never made the Office 365 web app.
So the problem for Microsoft is that whichever way they go, they will get less revenue from Office in the future, whether that's because more people will prefer cheaper alternatives like Google Docs or even their own Office 365, or because they have to dramatically lower the price for the "native" versions on iOS and Android, or because most people on these platforms, won't care as much about Microsoft's Office, because there are good enough (or free/much cheaper) alternatives.
I think in the end they will get less revenue because of a combination of both not being as relevant on competing platforms, and having to compete on a much cheaper price level.