She destroyed the colt, the weapon they were going to use to kill her, they thought they had no other choice but the Colt... and they were mistaken. Jack came along through Cas, and killed her.
They destroyed the egg, the weapon they were going to use to kill them, they thought they had no other choice but that egg... and they were mistaken. Jack came along and killed him.
Now the equalizer supposedly was the only weapon who could kill Chuck, and it's destroyed. Now I wonder... who could be the only one with the power enough to kill him?
¯\_(ツ)_/¯
Such a fucking mystery.