The example that sparked the discussion was that someone protects ships, shoots the pirate, then logs off. So the pirate could come back.
How about you simply tell the pirate that you shot in green: "Good fight. Please do not come back to harrass the people I protected. Feel free to come back to rp, but no piracy."
I mean... just talk to each other.
And... I don't think it is okay for the pirate that was killed to turn up as the "undead pirate, 2nd attempt" once the victorious defender logged off. From a roleplay pov, the attacker has been destroyed, the danger has been cleared.
But... as I said: just tell him and it is no problem.