Yeah I can't buy that unless your home game character is ridiculously overpowered.
I did what any respectable GM would do: Sic a dragon on him.
Specifically, the big angry one he fucked over who promised to get bloody, bloody revenge on all those who crossed him no matter how lightly they may have done so.
After, of course, using his guilt to rebuild GW's drake forces and running interference while Ghostwalker turned one of those uber shadow spirits into magic-WMDs. Even immortal elves get tired guarding an open planar gate to an insect spirit metaplane.
Harlequin is self-indulgent enough he probably understood the "double-cross" was coming the entire time. Keeping Harly alive post-stormfront seems like a premise thread to me. So I ended the threat.