Mike Sturgill explains how a stick in your deraileur can compensate for a broken derailleur cable

When the cable breaks, the derailleur springs force it to the smallest cog. In my case, that was an 11 tooth cog. Even on a flat road, an 11 is a stiff gear to push and my RPMs in my 39-11 were probably in the 70-75 range. This is much lower than my "comfortable" 85-95 cadence. What I did at the first sag was to first tie off the cable (it broke at the shift lever) so that it wouldn't flop into any moving parts. Next, I broke a limb off a tree and wedged them in part of the rear derailleur forcing it "up" a couple gears. So, I still couldn't shift the rear and it was single speed, but it was an easier gear to turn. In this gear, I could pedal about 95 RPMs at about 21 mph. This made things very comfortable for me.

If I didn't or couldn't get a cable, my backup plan was to continuously stop when necessary and force more sticks (or whatever) into the derailleur to put it in a gear that I could reasonable turn. I would have had to shift into the lower 3-4 gears to climb up to Sonoita, for example. This would certainly not be efficient, but would have allowed me to continue.

-Mike