Well, again, I'll be a blue-nosed gopher. This actually worked! I have a resurrected CPlay2Air unit now!
I did exactly as Denali outlined. After plugging into the lightning cable, I clicked "Update", it slowly worked its way from 0% to 100%, then gave me a spinning ring with the message "Upgrading, please be patient, this could take a while". It then reported, "Upgrade Complete". So I unplugged everything, took it back out to the truck and BAM, it came back to life! Head-unit saw it, and I was able to join it with my phone. All good!
Now here is the weird thing: After joining the adapter's WiFi manually in the truck, I navigated to 192.168.50.2 and it reported the firmware as 7.17 (which is what was on the adapter when I bricked it)! So I disconnected, and reconnected via Bluetooth (which then handed off to WiFi) and re-navigated to 192.168.50.2 and it is now offering to "Discover a new version..." to 2020.08.04.xxxx. I was too scaredy-cat to try another OTA update, so I shut down and have brought everything in the house to do a manual USB update to 2020.08.04 and see if that works.
So, to sum up, I am not totally sure exactly HOW this works, but it certainly does. I had a totally unresponsive, completely dead / bricked, CPlay2Air adapter, that would show absolutely ZERO lights, in the truck or when plugged into a power adapter, that now is working again. And while I'll be the first to admit that I was very skeptical about this technique, given my years of experience with networking and routing, I am extremely happy to report that it works! Or at least it did for my bricked unit. YMMV.
@2018 Denali, I don't know what kinda cereal you eat for breakfast, but it must be the "breakfast of champions", because once again, you my friend, "are da freakin' man"!