He's got a +4 Constitution belt, though not one that began from a very lofty beginning, and started out with 87 HP -- in Merrin's terms, a frankly inhuman ability to resist damage that isn't suffocation -- and also there's a Ring of Sustenance firmly on one finger, and an Amulet of Natural Armor that's firmly beneath his regular armor. He will be shockingly warm to the touch on account of his lasting Endure Elements -- which isn't actually helpful from the standpoint of oxygen deprivation! -- but also he's had one more minute of breathing than she thinks he's had.
However her Breath of Life-like supernatural ability works -- though she is taking the name weirdly literally -- she's going to be rolling against an unexpectedly low DC.