What happens if you don't use RemoveHandler?

Just asking for a friend…

As I, sorry my friend, opens a Window he defines a set of AddHandlers to certain Objects. There is no corresponding RemoveHandler in the Windows.Close event. When he closes this Window nothing seems to happen. Even if the Window is opened and closed multiple times, nothing happens.

Is this likely to cause future errors eg memory conflicts, plagues of frogs, etc?

The source object leaks and if the target goes away, your app crashes.