Have you tried monodevelop? Mono is a free open source version of c# and it works very well on windows, mac, and linux.
The Mono situation is actually pretty ideal practically, because much of what would be patented is known and not submarine patents, and it would be far harder than you suggest for Microsoft to start suing over that stuff after issuing their legally binding patent promise.
It's a given that Objective-C is entirely within Apple's domain and C# is within Microsoft's just as Java is now Oracle's. These languages are not independent of the organizations involved.
Other more standard-based languages, which has traditionally included things like C, C++, JavaScript and now Ruby are less likely to be disrupted because of shared ownership.
I'm worried about all the people chugging C# Kool-Aid when Microsoft wasn't the least bit concerned about taking SilverLight back out behind the barn...
Silverlight could only be killed like it was because it's on the client. Classic ASP, a 15 year old technology, still runs easily on IIS 8 / Windows 8. Yes, Microsoft could kill CLI on the desktop and stop distributing .net frameworks (or by removing the desktop mode from Windows 9 and removing .NET support from metro etc), but it's almost as safe a bet as there is that you'll be able to use it on the server for at least the next decade.