5e AID extends 5HP to maximum HP for 8 hours upon casting, using 2MP.
I changed it so it automatically extends temporary HP for 24 hours, once per day for free and cannot be cast separately.
If you take damage, temporary HP is taken first and does not return when you heal. It will only return at dawn and does not stack if there is some left.
Since temporary HP always is removed first, you will never have a scenario that it runs out.
In the vanilla spell if it expired and you had 5 or less HP, you would fall unconscious but stable. If you were already downed and within 5HP of the negative of your maximum HP then yes, you would die. It's moot because I changed the spell.