Keeping Windows 8 (PC) and Windows 8 Mobile in step through more than 1 or 2 upgrade cycles will take real determination and a lot of compromises. So much so that I'm not sure it's worth it. Similarity of look and feel might be enough. And Auto Sync (see my earlier post).
Staying alive is an altogether different kettle of fish. I really can't see Nokia surviving with what Microsoft are giving them. I waited a long time for Windows Mobile 7 and while I stuck with it, I was in the main, pretty appalled by what eventually arrived (even after Mango). All the things that were wrong with WinMob7 have been documented and I'm not going to recite them here,
Suffice to say I waited (and waited, and waited) for WinMob8 only to get a clunker. What MS have spent 2 years doing is beyond me. Some fiddling around the edges but no show stoppers, no game changers such that it isn't immediately obvious what, if anything, has changed between the versions.
In tying up with MS Nokia have nailed themselves to a turd and will, inevitably, end up, in a last shake of the dice, a Me Too Android phone maker.