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?
IF you are looking for reasons to convert them, I can think of a few. These don't necessarily mean you should, these are just possible reasons in the "recode" corner.

Maintainability

If you have a dev-shop that is primarily C# focused, then have python applications around may not be useful for maintainability reasons. It would mean that they need to keep python staffers around (assuming it's a complicated app) in order to maintain it. This probably isn't a restriction they want, especially if they don't intend to write anything in python from here on out.

Consistency

This sort of falls under maintainability, but it is of a different flavour. If they wanted to integrate part of this (python) application into a C# application, but not the whole thing, it's possible to write some boilerplate code, but again, that's messy to maintain. Ultimately, you would want to code of P_App to be able to be seamlessly integrated into C#_App, and not have to run them separately. 

On the other side of the coin, it is fair to point out that you are throwing time and money at converting something which already works.
Is there any good reason to convert an app written in python to c#?