If Karlsson left for actual legitimate hockey-related reasons, then whatever. It is what it is. That's the NHL these days.
If Karlsson left, like the question suggests, as a DIRECT RESULT of Melnyk... as in, it could have been entirely avoided otherwise but Melnyk's ego or some other unnecessary shenanigans chased him away... then I'd probably have a hard time giving money to the team for a while. I wouldn't stop being a fan in general, but I might second-guess things like ticket purchases, for instance.