You will not get any operation of electric hydraulic pumps when windmilling. The AC supply will fail on you- a windmilling engine will not still supply AC. The battery will just supply up to 30 minutes of emergency supply for minimal lighting and instruments. The windmilling engines at low flying speed will still supply enough hydraulic pressure through the engine driven pumps to power the control surfaces. Flaps and undercarriage should still operate through 2 of the hydraulic systems allowing flying controls to still function through the other 2 systems.
A 4-engine failure scenario is not practiced on the 747 as it is considered out of the bounds of probability. Twin jet pilots do practice total engine failure landings (and great fun they are too!)
A diagram of a 747 style hydraulic system can be found at
http://www.patprojects.org/dec98sca/av1b_2.htm It shows the complexity and sharing out of services between the 4 systems