I think the place where this falls apart a bit is that you threatened to report the player for leeching to begin with. My wife and I use the "Hey <playername>, you coming?" in party chat to test the waters first. If we get a parade of jerkish responses from the rest of the party we can assume that they grouped together and either leave or deal with it (if they ever were to get abusive in their responses, we'd report it, but none have gotten there yet).

If you see players trying to get the group wiped (and they admit to it in the chat window), that the GM can do something about. Leeching? Not as much.