1. Tomoya recalls (or nagisa reminds him) what he said to Nagisa in 1st ep season 1 and he realizes that change is natural and he should move on. Ushio stays dead. This ending would suck shit.
2. Tomoya instead calls out Nagisa's name, she thanks him and they have a talk or something. Flash back to reality and the light Tomoya got flies out and materializes into nagisa before flowing into Ushio, who promptly wakes up. This ending would be better but I still wouldn't like it.
3. Somehow, Tomoya gathered all the lights, calls out Nagisa's name, ends up back at her side when she gives child birth but she lives this time and they all live happily ever after. I would love this ending because I'm an optimist
4. Tomoya dies too. I'd kill people and would never forgive kyoani.
5. He meets the dying girl in that other world and she tells him to collect more lights, Tomoya gets a "new game +" prompt and begins the entire story all over again. I'd actually like this end; at least it would suggest that he's actually successful
However, I'm fairly certain a couple of these events will occur: They explain that the "lights" are the wishes of the town and something magical happens. The girl in the dream world "stops moving" (becomes a popsicle) but explains to robo-tomoya what he has to do in order to save either Ushio or Nagisa (this happens to get the true ending and good ending in Clannad). Tomoya calls out Nagisa's name as she's walking away from the school, she turns around and thanks Tomoya for calling her name. They suggest that Nagisa could never hate any one because all of the town people were like family to her and she regarded it all as a "dango daikazoku".
EDIT: I am a fucking genius