3 ways this could go down
Goku kills "Aizen" then realises his mistake, kills real aizen and wishes superman back with the dragonballs. then they fight and everything dies
Superman kills "Aizen" then realises his mistake, kills real aizen and reverses time to bring goku back to life. then they fight and everything dies.
Goku and Superman beat each other to death, and destroy the planet, and aizen, in the process.
Goku and superman are on completely different levels to aizen. once one is dead, the other will wreak Aizen, if he wasnt killed in the crossfire.