When a champion gives a challenger a shot and loses, should the challenger give the champ a rematch?

I think it's good for boxing when you rematches are made. But sometimes, an older (or younger) champ will face some up comer, lose and then be written off or fade into obscurity. Case in point, Viloria was just "upset" in the Philippines. Should the unheralded fighter be expected to give the former champ a rematch or is he justified in pursuing another fighter such as Ivan Calderon, who was expected to possibly face Viloria in his next bout?