Ok well I'm not really sure how it happened but when your in the Hollow and your about to go up the towner with the patrol on the side. The one where Marcus is saying "Anyone need sniper practice". Well at one point Carmine might try to jump over the rockworm and instead of getting over it he's on top off it! And when the worm goes in to his cave instead of Carmine getting pushed off he will go inside the cave with him! But you havn't lost him forever, later when you reach the top and then the cheackpoint happens he will spawn infront of you