.NET is under MIT license (https://github.com/Microsoft/dotnet/blob/master/LICENSE) and there's also a patent promise (https://msdn.microsoft.com/en-us/openspecifications/dn646766). There isn't an "enterprise .NET" version for sale. There are enterprise versions of Visual Studio, servers, etc., but nothing you could feasibly be "accidentally" using, and nothing that you have to use to do .NET dev.

What specific risk(s) are you thinking about?

Disclaimer: Microsoft employee, Nazgûl

Could change but I think Bill Gates originally tried making money selling a version of BASIC. Never made much money[1]. Since then Microsoft doesn't try to make money on dev tools. The dev tool business is there to support Microsoft's internal needs and to promote the Windows Platform.

[1] Bunch of companies tried selling compilers with 'drink your milk shake' licensing terms in the 80's. Developer resistance, Microsoft and Borland killed them off.

Dotnet is fully open source (mit licensed) for more than a year now. Let's just say I knew which of the two ecosystems to pick half a year ago for a new project. Java (as an ecosystem) is going down the drain as oracle has no clue what the dev world wants and where they are pivoting towards. Commercial frameworks and commercial languages are fast on their way out.

I doubt most enterprises would be willing to go back to C++.

C++ is as much as dead in the enterprise outside of a few niche concerns. It's just too hard to get right.

C# and Java are significantly more forgiving and for most use cases are perfectly adequate. Performance is a reasonable concern, but not the primary driver of language choice.

If you look at the sort of Java code some people churn out in an enterprise environment you'd be glad they weren't using C++ which has significantly more sharp edges. Throwing random exceptions isn't as bad as periodically segfaulting for no apparent reason.

The most recent example of this was Android Things.

Brillo was supposed to have key Android frameworks made available in C++, as explained at set of Linux Embedded talks.

Instead what happened was they brought in the Android Java frameworks and renamed it to Android Things.