You're a life saver! THANK YOU!
Good news: It's back home, and the immobilizer/central locking is working... For now
Other news: I need to figure out what the problem is/was, which I can do at home. An intermittent issue is the worst kind, as we know, because it can rear its ugly head at any time. Happily, I was only a few miles from home.

I used the shift lock override button to get it going. Once I was moving, the central locking and directionals worked without issue - no blinking trailer light in the gauge cluster, etc. Once I got home, the central locking and immobilizer LED seem to work fine now. I'll tinker with it over the next few weeks and will post the solution here.

 

Alrighty, just a quick update for the masses, but a rather anti-climactic update. I've been continuing to drive my Disco almost daily ever since my immobilization issue occurred (about 4-5 weeks now), and the issue has not repeated itself. This includes short trips around town, longer trips (a few hundred miles) across the state, and everything in between. I suppose it's good news, but also slightly unnerving news, as there's no telling what caused it or when it might happen again.

As a refresher, all I did was swap the battery and drive it home, as described above I'll post in here if I learn anything new, but for now, I'm going to operate business-as-usual and hope the gremlin doesn't return.

 

I turned a corner ... the car shut off without warning .. restarted and never happened again. Could never find the cause...

If I was you.. I would get a NANOCOM and disable the entire alarm system much as possible and replace it with a tracking device... when your battery goes down or out ... the car can be immobilized.

It's a PIA to deal with .. if I could remove the entire alarm system I would .. Alarm is too sophisticated for it's own good ..IMHO you don't even need it ...because most thieves would return the car after they see the gasoline fill ups and repair bills.

Maybe you can get a NANOCOM and shut everything off..