When I am on DRG, and I use Restoring Breath, if the monster dies before the ability goes off, then the ability doesn't activate and the timer is down as if it went off. From what I understand, the same thing occurs when using a SMN blood pact.

Example:

Player1 uses Restoring Breath.
Wyvern1 readies Curing Breath IV.
Player1 defeats Monster1.
(No curing breath)

Then I am forced to wait until the timer resets to use the ability.