Well, first of all the crew could commit to a certain amount of runway remaining after which there needs to be a G/A if not landed and secondly this "gate" could be easily programmable and given out with a synthetic command "G/A".
This would be no issue at all with todays computers. Even as a standalone machine if the avionic suite of older models wouldnīt be able to accommodate the required mods.
But then of course, this was a freighter and with no fatalities in "sufficient quantities" we canīt expect authorities to act. They rather let us fill in risk assessments, which for Bergamo surely finds nothing out of the ordinary....