The virus is already in us. Even if we die of natural causes we turn. Even if there is a cure, with the paltry number of humans left and no means of worldwide transport, the cure would only reach a limited few. The cure could not bring the dead back, it could only remive the infection in the living. So eventually you would have thise who wontt turn because of natural death but you will still gave the vast majority of humans walking dead. So, as i see it, slowly but surely each member of the group would be killed either by walkers or humans. In the end only Rick, Carl and Judith would be alive and in an act of defiance or protection, Carl would be bitten in an attack. Rick would kill him before he turned and then Judith, lastly he would place the gun to his temple as the screen fades to black.