Nah, you’re incorrect.
The shotgun shells were healed.
The missing arm was healed and the blood loss stopped. A severed arm does not kill you. Many people in the real world with missing limbs.
He was back in his ship, I am sure there own ship had the appropriate atmosphere but who knows.
What Harrigan did is not really relevant to the pred ending up dead from a slice.
There is no big difference. The gut slice is the only factor that killed him, nothing else did it. Its just like in the predators movie where a SUPER predator goes down from a Katana slice from a Yakuza ffs.