I been thinking, what if Lex stayed on through seasons 8,9, and 10, how that would've changed the series? With Lex knowing Clark's secret, I wonder if Clark would ask Jor-El to take that out of Lex's mind, or if not that, him using Clark to his advantage or he would expose his secret to the world. And if Doomsday and Zod would've showed up in Smallville. I could see Lex joining forces with Zod, but it would've been very interesting to see Lex in the face of Doomsday, lol.
Edit: Then again, I bet, Lex would've been in a coma for most of season 8 after surviving the collapse of the Fortress and if he came out of it, he probably would have memory lapses where he forgot Clark's secret. And upon seeing Doomsday, that would've been his new obsession. Then in season 9, Zod would be his new obsession and probably sometime in season 10, he would've discovered Clark's secret.