How much of a chance do they need? It's been 13 years. Should they wait another 5 years? Another 10 years? Another 13 years for her to be "rehabilitated"?
At what point do they become the selfish ones? How does anyone know whether or not husband and wife discussed 'quality of life' issues in the event of this type of situation. Perhaps she did tell him she didn't want any extraordinary measures performed.
Perhaps the husband is motivated by monitary issues. Or perhaps, he knows his wife's heart better than the parents do.