TBs maths is OK for a wings level entry, using a dFPV/dt, V input, to determine a g loading, but anything that achieves that in a wings level condition is a seriously catastrophic event,
And a bizzare one for that matter. I do not see many mechanical ways to end up with a proper wings level 0g nose dive from cruise. Trim runaway with full ND deflection and then the AP letting go would rather end up with negative g and seems also extremely unlikely. Why would the trim want to do that? Mis- trim scenarios did happen in the past but that was typically at low speeds, e.g. during approach but at cruise speed???
Losing Vertical tail will involve yaw/roll (could potentially be the case but the trajectory speeds >M0,9 do not smell like any kind of tumbling). Losing horizontal tail at cruise speeds would lead to massive negative g and shedding wings downward. Terminal angle being 90°ish. Jackscrew nut leeting go. That might hypothetically be possible. But in a seven y/o aircraft?? And then, why exactly at TOD? why suddenly and fully in one go without any prior 'warning'? In the case of the Alaska MD the failure developed over some time. The flight profile here appeared absolutely clean until the drop.
I'm somewhat struggling to conceive a 'hard' mechanical failure leading to the profile we apparently have seen here.