7 hours shouldn't mean death as long as the roots have water. Theyll droop some but should bounce back fine the next day.
As long as they dont dry out over that time, you'll be fine. You could raise your water level up to make sure they all have roots in the water or go around and manually make sure the roots stay wet with a spray bottle or something.
Passed that, I would also recommend some kind of battery pack and a small pump just to keep things moving.