(Am IR pilot) Assuming someone is paying any attention, the autopilot suddenly nosing down and the vertical speed increasing would immediately result in missed approach procedures being executed. These approaches usually terminate at a pre-determined height (decision height) which unless you're flying CAT-IIIC (not really used) is minimum around 50ft and more commonly between 100 and 200ft. Therefore you have some room for error in the event something bad happens. Additionally, approach paths won't have any protruding objects within a certain range of the runway.
Former commercial pilot here: we user to be doing IIIC approaches at least 3 times a year.
For the rest, usually below 10.000 feet, there van never be "two heads up", so one pilot is always watching the instruments. Any deviation from expected parameters (airspeed, verticale speed, ils deviation, radio altitude) Will result in an unstabilised approach and thus the execution of missed approach procedures (a go-around).
As mentioned elsewhere, everyone in aviation knows these systems are as insecure as can be.
