I would put my money on Tergat in a head to head. The fact MJ has run 19.3 is the reason he wouldn'y win. You need a hell of a lot of fast twitch fibers to run that time, so a 50 second openning will kill him. If the first lap was 52/53 then MJ could go well on the second lap and even run 1.46.
So, for Tergat to win he has to take it out hard, I would say he could do a 48 high and go through a second off that. If MJ goes with him, Tergat wins, if MJ sits off the pace and goes through in 53 will fly by him in the last 150m. It just comes down to MJ controlling himself in the first lap. 49/50 will seem so slow to him, he will think he is going slower than he is until the wheels come off at on the back straight. Winning time 1.47.2 Tergat, MJ DNF
Running a 800m is not about running a fast 400m it is about running two of them.