While we are throwing the speculative mud at the wall, I was wondering what single point failure could take out ACARS and the radios ... the BPCU.

All modern jets have them, have to. Their failure has rendered a 747, a 787 and other types completely unpowered. My concerns aren't for the 777, but the 787 where truly immense levels of electrical power go through a computer controlled box of mechanical relays.

A dark jet, no nav capability, turn towards land ... been there myself.