Anyone have an idea how a Triple 7 would behave with a complete electrical failure?
I don't think it would simply roll over. If the throttles & flight controls were not touched, natural stability should leave it doing small phugoid oscillations and perhaps gradually turning. I believe the fuel system would likely continue to deliver fuel and the engines would continue to run until the feeding tank ran dry.
Just theorizing a bit, but if the cockpit were breached in some significant way, not only would you lose pressurization, you would likely lose some of the functions normally controlled from the cockpit. A crew would be at a serious disadvantage to do anything meaningful.
The radar returns from the point in space where the aircraft ceased its squawk should be closely scrutinized for evidence of loss of panels or structure. If there is such evidence, then these items would be an absolute priority for attempted recovery since they would probably indicate what happened.
If the aircraft has flown as far as it is capable of after the deviation event, then finding it in a large expanse of ocean is going to involve a lot of luck. That aircraft may look big standing next to it but it is entirely possible to lose it and not find it for years.