Thug- Those're a lot of interesting ideas of how Harrigan might react to funding our about a hit on him. Honestly, he strikes me as a "Kill them all" kind of guy, but let it unfold how you wish. Make sure that Harrigan dies in some manner that will give the PC's a level of satisfaction at having solved a problem with outside the box thinking, be it having him murder through a score of assassins, surviving only by employing super paranoid precautions only to be brought down by a lucky blow (signifying that he really would have been a scary person to go head to head with), or by randomly dying in a humiliating fashion in front of his peers (letting them lol at his expense). I would try to avoid "he and his ship mysteriously vanished" as then they might be constantly thinking that he'll return later. How the learn of his death could be anything from a rumor in a tavern, to an ally learns of it, to a Red Mantis showing up to say "It is done.". Though that last gives them no details. But yeah, all kinds of fun to be had. I'd be excited to learn how this all goes down.