If you have a normal/emergency circuit set up to power fixtures that are being controlled by an Intelligent Junction box and there is a loss of power, it would depend on how the intelligent junction box is powered as to whether the lights would stay off or not.
The Intelligent Junction Box tells the ballast what to do and the ballast is designed to go to full brightness if it loses communication with the IJB box controlling it.
The normal way to power an emergency fixture situation is to have the IJB receiving normal power and the fixtures (the ones designated as emergency fixtures) to be powered by a normal/emergency generator circuit via a S5JS (Joiner Splice). In the case of a power failure, the normal emergency circuit would supply the power to the fixtures and the power to the IJB would be interrupted. The fixtures powered by the normal/emergency circuit would go to full brightness regardless if they were on or off before the power failure.
If the Intelligent Junction Box AND fixtures are powered by the same normal/emergency circuit, there would be no change in the status or level of the fixtures on that circuit.