NotAnExpert;
would ACARS send error messages stating that the computers had failed?
No, the message sent would be that the computers had been turned OFF. ACARS reports of failure modes are almost always accompanied with text messages of the fault(s).
That said, there are no procedures in place for the crew to turn the flight computers, (PRIMs, SECs) off to "gain control of the airplane" - it doesn't work that way on any 320/330/340 type. The QF experience may or may not modify that.