Does an A320 revert to Direct Law if both engines flame out?
The airplane will no longer be in normal law mode if both engines fail and no other electrical generator is online.

The airplane needs a primary source of electrical power in order to remain in normal law (among other things of course). If both engines lose power, then the generators on those engines also lose power. The only other primary electrical source is the APU generator. In addition to the batteries, the RAT (ram air turbine) is also available to supply electric power (along with hydraulic power) in an emergency situation. In this mode, the flight controls reconfigure to alternate law until a generator is brought back online.

From the US Airways 1549 report, page 88:


  ...the captain started the APU, which improved the outcome of the ditching by ensuring that a primary source of electrical power was available to the airplane and that the airplane remained in normal law and maintained the flight envelope protections