Right now obviously the content feed and the users contributing are low enough so they could be merged effectively.
In case the Fediverse and this instance grow rapidly though, I think that 2 communities would be more beneficial: having a more active community about C#, with questions about the language, its syntax, each new feature introduced etc, while the .NET community would undoubtly see less content and focus more on the underlying framework, the toolchain, language-agnostic discussions... In my experience, this is how it worked on the subreddits of the same names.
Do you want to have a banner added on the sidebar, redirecting to /c/dotnet until we grow larger? Does Lemmy have a polling functionality (to ask the user opinions)? I couldn't find anything.
LEAVE AS IT IS: Two separate communities, no merging