What would be the required altitude/airspeed to abort a landing? I'd think that could be done with anything down to the recommended airspeed and 50' altitude; is that correct?
If you can't land in the first 3000 feet of the runway most operators consider the landing to be beyond the touchdown zone, which would dictate a go-around.
A three degree glideslope is normal. That is also the glideslope angle for runway 31C at Midway. The normal glideslope intercept point for an ILS is about 900 feet down the runway; with the flare the airplane would land beyond that, at about 1500 feet or less. So 200 feet high (250-50) on a 3.0 degree glideslope (about 300 feet/mile descent) would have them landing 2/3 of a nautical mile long, or about 4000 feet long. This added to 1500 is well beyond a normal touchdown zone, about 5500 feet down the 6,520 foot runway. Even with some drastic last-minute corrections after crossing the threshold they would have been way too high to land safely.
YOu can abort the landing even till touchdown if you see you are long, you have plenty of speed to go around until you activate the thrust reversers.