does a hydro assist have the power to steer a truck ( toyota 4runner ) if you were to break a pitman arm ? The steering box will still turn and direct the fluid to the cyl, but does it have the power to steer the truck without the help of the box ? It would be a stock toyota ps pump. What about other vehicles or a different , stock or modifined stock pump ?

Yes I would bet it would do it.
The problem would be that it wont turn until the wheel is turned all the way to the stop because there won't be any pressure to speak of untli the box hit the limit. At that point all the pressure will go to the ram and then move the tierod. It might get you off the trail but that is about it.

I've never tried this, but it should work. :)
If you chain or bind the pitman arm in one position (like at full lock) so it can't turn, you should be able to limp out using hydro only. The torque on the wheel will open the valves and run the ram. If you left the pitman arm loose, you would have to spin the wheel all the way 'till the box bottoms to get the torque to open the valve and operate the ram..:D