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Growing up is hard to do — even for the kids of Glee.

After graduating from McKinley High last spring, Rachel, Kurt and the rest of the seniors are going to have a tough time in the "real world" when the show returns this fall (Sept. 13 at 9/8c).

"That's what this season is about, to me — going from this very cozy, family environment where it's all about following your dreams and then all of a sudden that's done and you're expected to go out into the real world and try to make it work and try to pay rent," executive producer Ian Brennan told reporters at Comic-Con Saturday. "What does it mean when you tell kids to follow your dreams no matter how hard it is but then it's really hard."

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Despite their win at Nationals, New Directions will also encounter some bumps in the road — particularly in replacing the seniors. "They're the underdogs again," he said. "The glow of them winning Nationals lasts for about two minutes and they're back to the bottom and desperate to find people to join the club." So who's going to join the New Directions? And who's not coming back? The executive producers and cast revealed what they could about what's ahead in Season 4 at McKinley, NYADA and beyond:

1. Kurt Hummel to the rescue. Kurt will return to his old stomping grounds in the first episode to help Will recruit new glee clubbers. "He's the one person who's sort of aimless and it's a little heartbreaking, but he's Kurt Hummel and Kurt Hummel lands on his feet," Brennan said. Executive producer Brad Falchuk hinted he won't be in Lima forever. "How long is Kurt going to stay away from his best friend? Not very long."

2. The seniors are going to have to step up. But will they be able to? "A lot of them have complained a lot about, 'I want the solo. I want to be the star.' Now the expectation is, 'Well now you have to do it,'" Falchuk said. "There can be stress in that. There can be competition there because people have visions of what they are and what they are capable of and what they expect to be given." Darren Criss, however, would like to see Blaine take a more backseat role. "My hope is that he's just another part of the team. I don't want him to be Blaine and try to take over things," Criss said. "I just keep making fun of Blaine because he's got to calm down. Just be a team player, guy."

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3. Sugar and Sam are in, Rory is out. Producers confirmed that Sugar Motto will return and that they're "in talks" to bring Chord Overstreet, aka Sam Evans, on full time. But Rory Flanagan will not be back this fall. "The second half of the season, who knows," Falchuk said of Damian McGinty, but hinted at possible encores for fellow The Glee Project alums Samuel Larsen and Alex Newell, who played Joe and Unique, respectively.

4. Watch out for the new kids. Although they can't say who won this season of The Glee Project, producers didn't shy away from bragging about the new cast member. "I'm excited for that person to come down the pipe because it was a real find and a big talent. I think we've found a star," Brennan said. The other new additions aren't so bad either. "We're still casting them, but we've got really, really good options," Brennan said. "[There's] a lot of just really talented actors who are coming in."

5. Sue's having her baby. "When we come back in, Sue has had her baby although we still don't know who the celebrity father of her child is," Brennan said, adding that the mystery man will probably be revealed within the first half of Season 4. "She's now Sue with a baby and a different set of priorities but she still can't help but make fun of everyone as often as possible." That includes Roz Washington, who will be back despite NeNe Leakes' series regular role on NBC's freshman comedy The New Normal. "They've got their eye on Figgins," Brennan said. "It finally occurred to someone, 'My God, this guy is totally inept and a thorn in everyone's side. Let's take him down.'"

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6. It's complicated for Rachel and Finn — and maybe Kurt and Blaine. Are they or aren't they? That's what everyone wants to know about "Finchel," including Rachel herself. She doesn't know "where things stand," Lea Michele said. "She's like what does this mean? Are we really broken up? Should I date other people? Where does this stand?" However, she has hopes for the couple down the road. "I can't do the show without working with Cory so I'm sure that we'll be together." Things could also go downhill for "Klaine." "It has to be one or the other — completely disastrous or completely awesome," Criss said. "Kurt and Blaine are getting a little ... too comfortable."

7. Santana isn't joining Rachel in New York... yet. Although fans last saw Santana decide to pursue her dreams of moving to New York to hit it big, thanks to money from her mom, producers told the crowd that Santana will be practicing her cheers at the University of Louisville come fall. However, her co-star has other ideas in store. "When you see Rachel in New York, she has a roommate that we've never met before," Michele said. But "Naya [Rivera] and I have been campaigning for Rachel and Santana to be roommates in New York for a very long time." As for the future of Santana and Brittany, Rivera is optimistic. "They definitely love each other, so I hope that they make it," Rivera said.

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8. Will's headed for a personal crisis. Will and Emma are still happily engaged, but it won't be all smooth sailing. "Will is struggling with the idea of what happens when the dog catches the car. They won Nationals, now what? And how his role with the kids has changed," Brennan said. "What that feels like when a teacher finally settles down and realizes, 'Oh my God, I'm a teacher for the rest of my life.'"

9. Rachel's new teacher is no Mr. Schue. "She is unforgiving as a teacher and likes to push and Rachel is not used to that," Falchuk said of Kate Hudson, who will play one of Rachel's "primary" instructors at NYADA. "She's used to positive reinforcement from Will so she gets pushed pretty hard by her."

10. Yes, everyone will be back. Really.  Just don't expect to see them as much. "All of the regulars from last year we got to come back in some capacity next year. Will they be back every episode? No," Falchuk said. "We're just going to be much focused on the storytelling. If it's a Puck story, it's a Puck story and he'll be back for those episodes."

Glee returns for Season 4 on Thursday, Sept. 13 at 9/8c on Fox.