I have written several Python tools for my company.  Is there any good reason to convert them from Python to C# now that their usefulness has been proven?  Would I be better off just leaving them in Python?
Changing languages just for the sake of changing languages is rarely a good idea.  If the app is doing its obj then let it do its job.  If you've got a corporate mandate to only use C#, that may be a different story (estimate the work involved, give the estimate to management, let them decide to pursue it or write up an exception).  Even if there isn't a strong (or any) knowledge of Python across the organization, developers are rather proficient at picking up new languages {it's a survival thing}, so that tends to be less of a concern.
Moral of the story, if an app is to be rewritten, there should really be more of a justification to do the rewrite than just to change languages.  If you were to add features that would be significantly easier to implement and maintain using another languages library/framework ... good justification.  If maintaining the environment/framework for one language is causing a significant operational expense that could be saved by a re-write, cool.  "Because our other code is in c#" ... not cool.
Is there any good reason to convert an app written in python to c#?