it wont. It only drains to where the water level is in the tank.
So when the power goes out, the tank drains till it looses sphion.
and the fuge drains till it matches the tank.
On my 75 i have a aquafuge by cpr. On my main tank i have a pinhole in my return so the tank only drains 3/4 inch. my fuge then drains to match that.
I've had my HOB fuge for about a year now with no problems.