Not a Prius owner but am curious about the regenerative braking. Does anyone know when in regenerative braking mode, do the friction(disk) brakes stay off until regenerative braking fades or do they combine with regenerative braking(blended braking)?

the brakes are normal, they dont have anythign to do with regeneration. The Prius regenerates electricity when you brake because its just transferring kinetic energy back to electric energy with its electric motor. It can also regenerate when you let go of the gas pedal, go downhill, when the gasoline engine recharges it, or even when the gasoline engine is pushing out too much power.