Well, as Astarion completely owns my heart as any white-haired character (Dante, I'm looking at you), I chose to forgive him. I mean: he literally killed me, but even so I forgave him.
To see whatever would happen, I did chose to threw him out of my camp and he indeed stayed there as I never punched him nor kicked him out in another savegame. So I guess it is bugged or they just didn't add his 'leaving scene' yet.
