Concluding the stage of negotiating the challenge to see who would be Kohen Gadol, Moshe makes a seemingly innocuous condition. He says in 16:29-30 that if they will die a normal death, that will show that “Hashem did not send me” and if something unusual would be the cause of death such as the ground opening its mouth and swallowing them alive that would prove these people incited wrongfully against God.
Both sides of Moshe’s condition were based on the death of his opponents. If they die normally he is wrong, and of they die in a freak manner, he is right. Seems one-sided to me!? What about a condition, if Aharon dies that shows he is wrong? Why did they have to die no matter what? It does not seem like a fair deal - if they are right they die and if they are wrong they die?
I guess Moshe knew most of them would die even if Korach was right and he was wrong. Only one person could have the job and with 260 or so people vying for it, most people would die. It was not just a matter of losing the job and having to start sending out your resume again to new potential employers. Moshe knew that all losers would die. It was just a matter of whether he or Korach was right. If Moshe was right, they would die a horrific death. If Korach was right, they would die normal deaths.