Just a thought but...
You gave it your best shot, aside from the fact that they casted dia on CFH mobs, which... I admit is quite disrespectful/rude. But, calling for help on Tiamat because you didn't want Kupo to take it at 20%? Based on what I hear, Kupo can probably take out Tiamat very quickly, so who cares if they start at 20% or 100%. You cannot say they don't deserve to start at 20%. They sat there and waited around 4 hours to fight Tiamat. Calling for help when a GM was already there? I wasn't surprised at all hearing that the LS ended up in jail.
Now, if there were a bunch of gil sellers or a competing newbie LS that might not have been able to win the fight from the full 100% -> 0%, then... Resetting the mob's HP is more justified, though still wrong. Certinaly, I would be annoyed if my LS wiped to Tiamat at 6%, and a newbie LS went up and used all their SPs to zerg rush a win.
Good job calling for help on a mob, right infront of a GM. It really builds your LS's reputation...
/em casts Invisible and returns to quietly reading BG forums.