You never want to trade the face of your franchise. Is Pablo that face? But you have to give value to get value. The Giants need a slugging first baseman, Dunn or Fielder. Either one could shift the balance in the west. What will it take to get either one? What about Pablo? is he part of the Giants future? is he too important in terms of marketing/paraphernalia sales?
What are the odds he will become a great player? is he the kind of player who succeeds at AT and T? is he destined to become a slow bulky first baseman? how many good years might he have? is his comedy wearing thin, or is he an important positive in the clubhouse? will he carry his weight well, or become injured? what about his speed? his GiDP? his plate discipline? Will his value decline? is this the best time to get value for him? who in the farm system would affect this decision? Would you rather trade him or MadBum? Cain? Sanchez plus??? What if Seattle would take him for Cliff Lee?
Realistically, I don't think Sabean would have the cajones to do it. But I think there is a case to be made.