Suppose a PC has been petrified, and the party cleric is
about to cast a break enchantment spell to bring him back.
Can the cleric first cast an endurance spell to boost the
petrified character’s Constitution score so that he or she
won’t fail the required Fortitude save to avoid death? Can
he be considered an ally (for the purposes of spells or effects
that help allies) even when in stone form? Is he even
considered a creature as far as the endurance spell is
concerned?
   First, when you restore a petrified creature with break
enchantment, no Fortitude save is required. The stone to flesh
spell requires the subject to make a Fortitude save (DC 15) to
survive the process, but break enchantment does not.
   A petrified creature is mindless and without senses, but it is
still a creature. For all intents and purposes, a petrified creature
is an immobile construct, and magical effects applied to it
function as they would if used on any other construct. Since a
construct has no Constitution score in the first place, it cannot
benefit from an endurance spell, or from any other effect that
increases Constitution. When a petrified creature receives a
stone to flesh spell, it uses its normal Constitution score for the
required Fortitude save. In the case of a stone to flesh spell, the
recipient first turns back to flesh (and regains its normal
creature type complete with Constitution score), then makes the
Fortitude save.