Ripped out my right rear in Moab this year and after crimping the hard line as best I could I still couldn't stop it from dripping completely and can confirm my experience was the same that you have zero brakes at that point. My e-brake works pretty good and the combo of that and downshifting the auto I got home without issue.

 

How do they do that when there's typically only one line that splits into two near the rear axle that feeds both rear brakes?

Edit: I guess with some modern ABS systems, each rear wheel has it's own feed. And diagonally, you would need two proportioning valves.

 

No. Abs is sensed on a wheel by wheel basis but when actuated it is just one motor driven on off rapidily pulsating on/off valve in the fluid line that helps any wheel from locking up in a panic stop situation. It works like pumping the brakes at 600 times per minute.

 

I don't see how the brake lock differential would work with a single on/off valve, I think you would need a valve for each wheel. Other ABS systems may work as you described, but I believe the JK system has a the ability to control a single wheel at a time, whether for traction or for ABS.

 

Well then crawl underneath and prove me wrong. Look under the hood at the abs motor....no valves. One pulsator motor.
Not saying I couldn't be wrong.

 

I learned something from the following videos. The motor is for building brake fluid pressure, and the solenoids control pressure at each wheel, individually. The ABS module has to build its own pressure to reapply the brakes since the pedal isn't being pumped, hence the need for a pressure pump driven by the motor. This also allows it to be used as a traction control device, since the pressure built by the motor is used. The solenoids control either releasing or applying brake fluid to the brake calliper.

https://www.youtube.com/watch?v=UUUbPo9pY1E https://www.youtube.com/watch?v=IKi5O3ZlSu4

 

So it seems like the only way to prevent this from happening is to swap out the master cylinder with a type with two individual reservoirs to not loose all of the fluid. That's only if this type would work with modern ABS systems.