I remember when Halor was on the ground, Ragnarr was debating using a saving throw to help him get back up, and then Ryan said something like “I’d decline the save”, due to it being such a penalty to fail a death save and you’d be better off no risking it.
Failed Saving Throw
Sometimes an effect changes as a target fails saving throws against it. The new effect, specified in a “First Failed Saving Throw” or a “Second Failed Saving Throw” entry, takes effect after the target fails a saving throw against the previous effect at the end of the target’s turn. The effect doesn’t change if the creature fails a saving throw against it at a time other than the end of its turn. (PH2, p. 219)
This means that for death saves (or any saves with a fail condition), you can only fail at the end. The bonus saves don’t count if you fail. Neato.
So that power (Divine Mettle…+5 to a Sv throw) can be applied to death saving throws. That’s a a 15 or more gets your life back.