Everyone is going to die. Yes, I said it. During this trip, Tomoya is going to lose Ushio. That is going to happen in this next esp. Then, depending on if they do a time skip or not, Tomoya is going to end his life. He lost everything, has nothing to live for and so on and so on... Now were at esp 19. Key / Duke [whom I got the information from, or I think at least..] said there was 24 esp's this season. You can't come out with the "real" Clannad ending, without having Tomoya / Ushio / Nagisa die in the story.
Worst comes to worst is the time they spend on this trip. From what it seems the esp's will be like this, Esp 18 - Tomoya starts to notice he's just like his father, tries to fix it, but loses Ushio right at the end. Esp 19 - Tomoya goes crazy and ends his life. Esp 20 till end of season - Story of the girl and who she is, along with how Tomoya is going to fix his mistakes and make everthing right.
If you noticed, they didn't come straight out and say Nagisa died. They filled us in with a 5 year time skip. Reason for this? To negate the side effect of losing fans from airing Nagisa death during the birth / shortly after. Yes, they were building this up for a long time with Nagisa being sick and all but it just so happens, during the game this is how you get the sad ending for Nagisa / Tomoya. If you remember, that esp ended a "toss up" of while Nagisa just passed out or was killed. I'd expect half of the viewers wouldn't assume she died, but with her health history, maybe I'm wrong.
All in all, I don't know how their going to pull this off. In the game you don't "learn" about the other world other then helping Nagisa with her play, and having Tomoya mention he knows of it but can't figure out where. Once you finish a story, any story. Your featured with a picture of a girl with a robot saying you didn't collect enough "lights" to have the real ending. And you need to restart the game and finish all the other stories, which most people haven't done. I spent about 15 hours total time played within the past 2 weeks and I only got one ending finished so far, with not even half way though the second.
All in all, with the amount of time left, and where the story is. It's only natural that they aren't going to end this with Nagisa / Tomoya / Ushio dieing like the movie. Unless there is only 21 esp.. then.. I'm not 100% sure anymore. [Forgive me its 2:50 am, and I'm not bothering to check :p]