Yes it is, plenty of other multiplayer games do this already. You kill task/drop connection in combat, you leave a ghost alive for X amount of minutes. Doesn't require a connection, the server can keep it there and count all the dmg done towards the ghost, and when the douchebag logs back in, the server sends the info on his client and "Your ship has exploded".
Fixed. And after that has been fixed, I'd raise the log off timer to infinite, with no possibility to log off from the game during combat. You resolve the situation with your skills (or you die and learn from your mistakes), not your log off speed.