not in our lifetime. mj was the only person that run 43.1 for the world record and split 42.9 in the world record 4x4 in 1993. i think it is almost impossible to run 42.5 which is a 20.7 200 followed by a 21.8 200. i am sure some people can open with a 20 high first 200, but they will come back with a 23-24 second 200, basically somebody will hand them a piano in the last 100 as larry rawson likes to say.
Usain Bolt of Jamaica is 16, 6-5, and has run 45.35 this season. He doesn't turn 17 until August 21. He looks like the most likely successor to MJ, and if anyone is going to go under 43, I think it will be a taller man like Bolt.