You are right, it's not a sinking ship. It already sunk. Who is using .NET and what the hell are they using it for? I'm sure there are insurance companies and other random boring Innotek organizations in non-tech focused companies still out there using .NET for equivalently boring software development. If you enjoy that that's cool. I don't. No one is advancing computer science, nobody is working at the brink using Microsoft technology. Including Microsoft. I'd love proof otherwise, because honestly I think C# and .NET is quite well designed. But I can't find any counterexamples.
Not sure if it "advances computer science" but Power Map is an IMO pretty cool app we shipped v1 of early this year which had its UI implemented (partly by me :) ) in WPF :). Even the 3D visualization engine was mostly C#.