The key problem was that they chucked the existing assets overboard while Windows wasn't ready.
Maemo/Meego was pretty much ready, the N700 was a decent tablet before the iPad was a twinkle in Job's eyes. I replaced my stolen iPod and Macbook with an N800 and a Bluetooth keyboard back in 2008, with 24GB of storage. Was perfectly serviceable, and would just have needed a bit of TLC to get up to the standards of Android tablets.
Jolla's Sailfish platform show what Nokia could have had, an independent platform that was good enough at the time which now runs android apps.
Basically, if Nokia had put the effort into Meego that they put into WM , I'm certain it would have turned out differently.
Then there's the fact that in Symbian , they had the most power efficient OS out there, which still has a certain caché.
Elop burned the platforms, he took on a company that was the biggest phone company (and smartphone...) and ended up as a small appendage of Microsoft .
That is not a successful outcome by any standard . The equivalent would be the CEO of Toyota running it into the ground so badly that it becomes a local subsidiary of GM