You definitely made the right decision, quick reaction to let it go. We have a lot of hills around here, different ball game at times, don't like thinking about when things don't go as planned, I have skidded down into the hegerow, but used the loader bucket to slow me down, scary business.
Years ago, boss sends me to a customer in the nearby mountains, 10 ton of stone, single axle F800, hydrovac brakes, 5+2 trans/rear, 370 gas engine. I got close to the top, but it stalled, I was in 2nd gear, but it was too much, I did not drive this truck all that much, so I did not know how it performed, I should have crept up in 1st which was really low. Brakes would not hold, I was rolling backward down a steep hill, with a drop off at the end. I let up on the clutch, it almost went over backward, I broke something in the rear, still going, I did not panic, but was scared like heck, steered it into the ditch, so the first move was a mistake, but the 2nd was the one I should have done first, and its that seemingly eternal juncture of time where you just react and that is what scares me the most, will you make the right decision, there is NO time to think, you definitely made the right call, glad you did not get hurt.
Boss, whom I am still friends with today, understood, should have taken the R model mack for this job. One lousy saturday am delivery, would have been done early, go back get lowboy and dozer, get truck out, dump load, load truck on trailer, bring to yard, go back, get dozer, ended up an all day affair. His dad made the repair to the rear end, ahd that truck been a diesel, and I have driven newer 800's with diesels, never would have stalled, that '80 was a gutless wonder with a 370 in it.