Microsoft isn't in decline, however much people like you and I would like to imagine them to be. Microsoft is in its prime as the premier desktop operating system and Windows 7 established this in granite. Windows 8 has hairballs, but they are in a position where they can make a mistake or 2 and be trusted to correct it and the market will forgive them for this faux pas. The alternatives to Windows offer no stability advantages --- Linux is far from "write once, works 3 years from now" and neither is OS X. You'll find greater stability in running a Windows app via WINE that you will a native OS X or Linux app several years down the road.
Don't shoot me --- I'm not even a messenger --- sure Windows isn't going to penetrate the mobile or even tablet market simply because they are clueless and in identity crissi, but they will own the desktop market for at least a decade or 2 and it could be more than that.
No, Google Apps is not going to defeat Office let alone automate corporate documents .... reality bites, but reality counts too ...