I think Carl will find a cure gun or shot and keep it with him without telling everyone and not even knowing its the cure. Later Rick gets bitten and turns into a walker. Carl finds the will to shoot or stab Rick with it. Rick will then as a walker start to shake and drop to the ground. He will be a human again. By the way again this is only what I think will happening. This is what I know will happen in season three or four. WARNING!!!!!!!! ~SPOILER~
Lori dies Rick finds Morgan again and finds that his son is a walker. Morgan is keeping him with him while he is a walker and killing people to feed him in the book known as "The Walking Dead Philosophy" The Governor will cut Ricks hand off in the comic.