Leave one alive outside and they won’t take off. But if you kill everyone inside, loot everything, and goes back out and take out the remaining guy, it will fly off despite everyone inside being dead.
I found the same ship in orbit after (a red enemy dot that didn’t attack got me curious), boarded, found them still dead but returned to their seats. And the illegal cargo on their dashboard having respawned. No loot in cargo or captain’s locker. It could have been a different ship, but that would be one hell of a coincidence, exact same ship layout, and missing cargo loot?