In Pathfinder, I am playing a 11th level Oracle/1st level vigilante who primarily uses a heavy crossbow with Crossbow Mastery. All crossbows require two hands to reload even Repeating Crossbows, which I am not proficient with. We are playing with the Critical Hit Deck and a major NPC got the severed hand card on me. So now I have no right hand. What are my options?
Your only official option to replace the hand would be to find someone to cast the Regenerate spell on you, assuming you still have the hand. The other methods of gaining a regeneration effect all seem to only fix limbs severed while already under the effects of the items - namely a Ring of Regeneration or a Trollblood Elixir.
You could also potentially replace the entire arm with a Necrograft.
If replacing or regrowing the arm isn't an option, then...you are probably limited to using retraining to replace whatever crossbow-related features your character might have, or retiring the character.