Converters that convert purple gems currently leave lycanthropy gems on the board. I haven’t checked them all, but have confirmed this using Moonsinger.
Given that lycanthropy gems are regarded as purple for matching, it would be more intuitive for them to be treated as purple for conversion too.
Players also need ways to counter lycanthropy gems, which (as discussed elsewhere) are an unwelcome match whether matched by the player or the “AI”.
[Edit: I regard this as a bug, but since I have never seen a statement of the intended behaviour I posted this as a Feature Request. A Bug Report for the same issue now exists: Purple converters not converting lycanthropy gems]