CoreCLR is open source now, so even if Microsoft abandoned it tomorrow, the community would keep maintaining it or worst case most of it would probably get merged into Mono.
This BSD port was mostly a community effort by the way.
I've recently decided to switch to .NET for everything. Mainly because I really like F#, and I've been using C# for a side project in Unity, but also because an open source CoreCLR makes me worry a lot less about vendor lock in.