Aced in the Hole is an important mission chiefly because it is the last chance to manually save your game (instead of relying on the auto-save). Sam Becker will warn you that once you commit to the mission, you cannot go back.
Take it as a hint and save the game if you wish to see all the endings in Far Cry 3.
Last Chance to Save
The last chance to save your game before trying to get the different endings is before speaking to Sam Becker to start this mission. Do it, or you will be sorry.
Mission Number: 36
Previous Mission: Black Gold
Following Mission: Betting Against the House
Rewards XP: -
