It helps that now most (if not all) parts of the stack are open source and run on Linux.
I might be biased from having worked with production F#, but it feels more like functional is making its way into C#, as the general industry sees value in functional principles. So F# feels like its more here to stay?
C#s adoption of language features shows their utility but they’re not a replacement, per se. Without a clear functional answer in certain language and parallel computing scenarios MS would be ignored. Scala and Kotlin are comparable answers to comparable pressures on the JVM, and even keeping pace there with new and exciting tools/libraries requires some proper functional representation on the .Net platform.
F# will disappear when/if those other languages do, and already has lots of what C# is chasing with a more elegant syntax. It inherits VM and project improvements from C#, so the biggest threat to long term investment is something like the crippling changes made to FSharp Interactive (FSI), during the .Net Core transition. Otherwise it seems to be in a safe place for the foreseeable future.