Bo Beck is a small-time captain of a light sloop, the Grim Reaper out of Rambleshack. Beck made a deal with Jolly Roger to deliver the imprisoned Captain Jack Sparrow to him when Jack made his escape from the Rambleshack jail.
But, Jack offered Bo more money and Beck went with the higher bidder. He was told to deliver someone else... in this case the player's pirate.
His final fate is unknown, but likely now he does the bidding of Jolly. As far as we can guess, he will not walk this world as a human again.
Bo Beck has not been seen in the game past this point. Jolly Roger may implicate him into the story in the future. For some reason it shows a similar looking pirate in the cutscene before the Black Pearl Boss Battle.