I hate to speculate about what Rono could have run; I think such speculations sometimes do an injustice to both Henry and the great runners who came after him. I really don't doubt the story about his drinking the night before the race and his subsequent hangover; I recall that Henry himself later joked that he was glad the track was round, because his head was spinning so much that he was just trying to keep up with it as he ran around the track that evening. That story was also consistent with what I've heard from directors of other races, where Henry ran spectacular times after drinking heavily the previous night.
The part about his near flat-out hour run that morning to "sweat out" the alcohol is also consistent with similar stories of his efforts to "sweat out" the previous night's alcohol with pre-race workouts. I think it was also consistent with his usual race-day preparations. Henry has said that, on the morning of his great 10,000-meter victory over Salazar in 1982, he did a very intense session of hill repetitions for forty-five minutes.
To me, one of the most amazing things about that 5,000-meter world record (and a number of Henry's other performances, including the 10,0000-meter race against Salazar) was how quickly Henry transformed himself from "hobby jogger" condition to world-class shape. In June 1981, he went over to Europe and entered a 5,000-meter race in Finland, where he got double-lapped. I think his time was 16-something; I remember seeing the results at the time. He spent the month of July training in Germany and losing weight. In August, he ran a series of races with increasingly quick times, including a 13:22 and, two days later, a 13:12 -- the season's best time. He then ran a season's best 10,000 and a season's best 3,000. In September, he broke his own world record at 5,000 meters.
Of course, it's likely that various inaccuracies and exaggerations have crept into stories about Henry Rono, but there are also a lot of reliable eyewitnesses and race results to back up some of the most unbelievable ones.