Kamina would've eventually developed his own Spiral Power, and be able to stand head to head without the constant "combine!", which he was already getting close to in episode 8. He would keep his idea to become someone who Simon respected, and strive to stand on his own.
In turn, Simon would gradually grow out of his dependance to Kamina, but gain some of his more hot-blooded qualities too, like he did after the timeskip. He too, would eventually be able to stand on his own.
And they still could've found Nia, with the Dai-Gurren moving in the box graveyard general area and stuff.