Stagger, I think you will find we already face those problems. On almost every widebody evacuation, someone is seriously injured (personal opinion). I think we will increasingly be facing fatalities from ultra large jets (2 candidates at the moment). It will be a difficult decision and I think will increasingly have to be made relying on external advice. Of course catastrophic events will make for an easier decision.
GD&L- retracting the gear prior to evacuating won't work:
*despite the best of intentions of engineers, gears are not designed to be retracted on the ground. I don't think hydraulics will be able to power the main gear out of 'down'.
*settling the aircraft when everybody is standing queueing to get out will have everybody over
*potential for damage/explosion (hot engines/fuel leaks from damaged tanks) too great- would likely cause further severe problems
*it would write off the aeroplane for possibly needless reasons.
*so it makes a 35' drop for the upper deck say 25-30' (personal guesses). Worth it? Aeroplane may tip tail down exacerbating the problem as the front inboard engines will take the load (before giving up).