takata - congratulations on some excellent and thorough work. I did ask 'the experts' a day or so ago which choice - continuing ahead or turning back through the weather - would be likely vis a vis ETOPS/fuel etc. and have had nothing back. Instinctively I think your 'turn-back' looks like a very likely scenario. Even your projected radius of turn is plausible.
I'd still like to focus on what was LEFT on the instrument panel for them following the known ACARS messages; whether there is some common electrical supply issue that could have caused these failures and whether there is a common 'software junction' in it all. What did the ?Air Caribe? have left in their incident? I cannot find any detailed report.