Is there an if/then/else operator for observables in c# available?

Yes there is one: https://github.com/Reactive-Extensions/Rx.NET/blob/develop/Rx.NET/Source/src/System.Reactive/Linq/Observable/If.cs

But why don't use your selfmade version? It seems to work quite well for me.

Sadly there is, as far as I know, no build in operator for this task in .Net.