I killed him during my current playthrough. When he attacked my Gith sorceress, I switched to SHadowheart and started a fight. Feels really good. His introduction scene is kind of messed up (which is the topic of another thread) in that he attacks you, but you only have the opportunity to forgive him. You can aggro most of the other companions for far less stuff, so I think, we should get the opportunity to aggro Astarion too - he is the only one outright attacking you.
"We are all stories in the end. Just make it a good one."
