I'm specifically looking at the spell Infuse With Vital Essence, but it would also be nice to know the answer generally speaking.
Infuse provides 50 bonus health and 50 bonus endurance for a reasonable duration, and my hope is that it'd be a useful sort of panic button for keeping my party's wizard alive in case he happens to get engaged by troublesome enemies like Shades and Phantoms. But I'm playing on Hard and often find myself running my party to the limits of their health pool, and unfortunately the game seems to offer no explanation for what happens after that temporary health or end