The final step of the combat phase for an active ship is dealing damage to the target. Once the attack is over, there's no evidence you're still active for dengar's ability. I would argue if dengar isn't active, no one is. If the ghost isn't active at the end of the phase when attacking with his turret, there's already precedent for there being no active ship at a given time (which I think is dumb, but if that's the argument).
I see what you mean, but Dengar's ability specifically says you can shoot the attacking ship. Gunner lets you change that target if you miss, but that attacking ship isn't the attacking ship if it's activation has ended.
Wait.
"Once per round after defending, if the attacker is inside your firing arc, you may perform an attack against that ship."
There is a dependent clause there (or something, I'm not an English teacher) but the phrase "the attacker is" is present tense which is what I am basing my argument on. There is the argument that they should have written it "the ship that had attacked is" but that takes more room. Guess it will take a FAQ after all.
This is why my earlier post that ubul was responding to specified dengar with gunner killing someone that hasnt' fired yet. You miss the first shot, gunner someone of the same PS that hasnt' fired yet to kil them.
