Attitude to Linux and open source was not really a problem for Ballmer IMO. Microsoft had vast revenues locked in to their software in PC and business servers. In the regulatory environment in which they were permitted to operate, it made a lot of sense to try to keep competitors out. A cohort of geeks hated Microsoft's attitude, but I'd be surprised if it did much to their bottom line. But Linux and OSS are just a tools, easily adopted when the winds change.

Microsoft under Ballmer completely missed the boat on a bunch of things which should have been pretty close to Microsoft's wheelhouse -- search, social media, mobile/smartphone, and cloud, to name some of the big ones (each one of these spawned a big 10 corporation). It's not that they should be expected to cover all these things or that no other tech company should have become successful, it's just that they had little response to any big developments in the industry for many years.

I think it's less that he wasn't willing to let go of Windows, more that the myopic focus on it blinded them to other issues, or deluded them into believing they could continue using Windows to gatekeep and buy or crush competition. They missed the boat on the internet before Ballmer too, but eventually managed to use the money and power that Windows provided them to grind down the competition.