If the world's ending had remained unchanged, Mizuki could have handed all the missions over to Sasuke Uchiha and Naruto Uzumaki long ago.
Team 7 was far stronger than in the original story. Even with the butterfly effects caused by Mizuki's actions, there was a good chance they could successfully seal the Ten-Tails.
Even if something unexpected happened, Mizuki would be watching at all times to set things right.
Mizuki had made many contingency plans long ago for the variables that might arise next. Naturally, they included the worst-case scenario: completely activating Dreamplay to cover the entire Shinobi World, fully converting illusion into reality and reality into illusion, and restarting the Shinobi World from scratch.
How difficult would that be?
One only had to look at the fate of Hagoromo Otsutsuki, the Sage of Six Paths, to understand the price of repairing the flaws in the world's rules.
This was not a problem that could be solved simply by manipulating chakra.
For a replacement of rules involving the entire world, even if Mizuki poured in his entire life, soul, and every physical clone, it might not be enough. Perhaps he would have to do something like Asura and Indra's chakra reincarnation, slowly mending the imperfect world and relying on time to heal every wound.
Although his will could continue in another form, it would no longer truly be his complete self.
As for the two children of destiny entrusted by the Sage of Six Paths with sealing the Ten-Tails, if they wanted to save the world from destruction and humanity from extinction, then of course they had to fight to the end and defeat their enemy.
"Where did Teacher Mizuki go? Why isn't he back yet?"
There were only so many living people in the entire Shinobi World who could