Re: What if Firefly had run for five seasons?
I think Simon hooking up with Kaylee would've equaled death for him (though it might still have been worth it...) also it would put River in an interesting situation, without her older brother to look out for her. So yeah, I think Simon would've eventually been killed off in the 2nd or 3rd season.
"I want to see gamma rays, I want to hear X-rays, and I want to smell dark matter. Iím a machine and I could know much more."
- Cavil, Battlestar Galactica