We need to clear up something first.
Slay Living grants you a touch attack as part of casting the spell to deliver it (thats an entire standard action). Unless the Hag is holding the charge (from a previous round), used a quickened spell like effect, or has an ability similar to Spell Strike, they won't be able to make a claw attack AND deliver the spell at the same time.
Assuming that no rules were misapplied leading into the attack, the hag must hit the target first in order to deliver the spell. That means rolling the claw attack (and damage for the claw attack) and then applying spell resistance (if any) and the fortitude save, before assigning damage from the spell.
Narratively speaking, it all happened in a moment. Following an order of operations, the player character was slain by loss of hit points from the Slay Living spell, and thus Breath of Life is insufficient to bring them back to life.
If rules were misapplied in the delivering of the spell (as noted above), it might be fair to just let the Breath of Life spell function this once.
As you did not specify HOW the hag was delivering the spell (Spell Strike or Holding the Charge), we will default to the most likely ruling that is to be applied in the situation. This covers a quickened spell 'effect' as well.
Holding the Charge: If you don’t discharge the spell in the round when you cast the spell, you can hold the charge indefinitely. You can continue to make touch attacks round after round. If you touch anything or anyone while holding a charge, even unintentionally, the spell discharges. If you cast another spell, the touch spell dissipates. You can touch one friend as a standard action or up to six friends as a full-round action. Alternatively, you may make a normal unarmed attack (or an attack with a natural weapon) while holding a charge. In this case, you aren’t considered armed and you provoke attacks of opportunity as normal for the attack. If your unarmed attack or natural weapon attack normally doesn’t provoke attacks of opportunity, neither does this attack. If the attack hits, you deal normal damage for your unarmed attack or natural weapon and the spell discharges. If the attack misses, you are still holding the charge.
Attack -> Weapon Damage -> Spell Effect -> Spell Resolution
This concludes in the death of the player character via a death effect.
I would say that the damage occurs simultaneously. The wording of holding a charge uses the word and not then. To me that indicates all damage occurs at the same time.
I would say that the damage occurs simultaneously. The wording of holding a charge uses the word and not then. To me that indicates all damage occurs at the same time.
I agree that it can be interpreted that way as well, though that does nothing to resolve the issue being discussed. The spell damage certainly does not occur BEFORE the weapon damage, as the weapon attack must land for damage to even occur (even if reduced by damage reduction, if any).
Whether simultaneous or not, an order must be decided so that interactions with other effects (like Breath of Life) can be arbitrated. To that end, I lean in favor of the weapon damage resolving first, as the spell must still interact with spell resistance (if any) and a saving throw.