Gear and flaps will be available, albeit at reduced rates, with all engs windmilling. This will not result in loss of control - system 2 & 3 hydraulics can handle flight controls while systems 1 & 4 are busy.
Again, perhaps you're talking about the 744, because the Classic's procedures are clear; do not use gear or flaps with windmilling hydraulics. The demand is great enough with gear that additional augmentation is required with the ADP. For that reason, with windmilling engines, hydraulic extention of gear or flaps will not be available.
Our procedure very clearly states "Do not operate flaps or gear."
If gear or flap operation is necessary, there's always alternate extention. There's obviously very little electricity available to do that, and it's not available for long.