I took some time to watch the video of this race today again and noticed a few interesting things about the race. He goes through the first 400m at 49.28, meaning he would just need to positive split a 50.71 to run 1:39.99. Obviously a tough thing to do, but not impossible. That's two more 200s in 25.35. He runs the 200m between 400 and 600 in 25.02 totaling 1:14.30! All he needs is to maintain that pace and even has the slightest cushion because at 1:14.30, he is averaging out to run a 1:39.06!
Here's the only and most epic fault in his performance (Ironic because it was a world record) He pulls out a 14.2 100m between 600m-700m putting him at ~1:28.5 and finishes the last stretch in 12.4.. Obviously the turn slows the runners down, but it can't slow you down that much can it? All he needed to do was run 25.69 (12.84 x2) which is actually slower than the previous 200m (The supposed hardest one) that he just ran.
Just something to think about.