Kate Walsh Kate Walsh

Private Practice kicks off its sixth season Tuesday (10/9c, ABC) with a sense of foreboding: The series was only renewed for 13 episodes, after which Kate Walsh will say farewell to Addison Montgomery and exit Seaside Wellness. Could the series go on? There is still a possibility, but executive producer Shonda Rhimes and the Private writers aren't pulling any punches in what could be the final season.

"I consider this to be our no-holds-barred season," Rhimes tells TVGuide.com. "Anything that we have ever wanted to do, we're going to do. There are no rules. There's not going to be a single episode of Private Practice that's considered a typical Private Practice episode. This is our chance to really have some fun, be creative and really make every episode an out-of-the-box episode, which is what we're doing."

Exclusive: Jack & Bobby alum Matt Long joins Private Practice

Still, Rhimes has not completely written off the series, noting that if she comes up with an idea for how it could continue without Walsh, she's game. But for now, Walsh really is going to exit. "It's been a really great ride," Walsh says. "Between Grey's and this show, it's been eight and a half seasons, and as awesome as it is and as much as I love every single person I work with from tip to tail, it just feels like I've got to see what's next for me."

In keeping with the no-holds-barred theme, many episodes will follow a specific character and their point of view in a Rashomon style of storytelling. "Every script is completely different from the format of the show last year and from each other in the season," says Caterina Scorsone, who plays Amelia Shepherd. "It's like they're pulling themes out of a hat, and every episode is this totally new idea." Adds Walsh: "Still, at the same time keeping the integrity intact."

The season premiere is actually a group-centric episode, with big questions being answered for several of the characters. Namely, who does Addison choose? The Season 5 finale left off with a choice for the doc: Accept Sam's (Taye Diggs) proposal or continue her new fling with Jake (Benjamin Bratt). So who did she choose? "Cooper. That's what's so weird," jokes Diggs, who quickly adds, "I should've said Violet!" Regardless of her choice, Diggs says that it will change the budding relationship between Sam and Jake this year. "Obviously there's going to be a bit of tension because as much as neither of them want to admit, it is a bit of a contest and there is ego involved, especially when you're dealing with love," he says.

Kate Walsh confirms exit: This is my last season of Private Practice

The series will also toy with jumps back and forth in time, enabling viewers to take a look at something that may have happened in the past with a fresh perspective. "There's a lot of stuff that comes full circle with characters that I think is going to be titillating for the audience," says KaDee Strickland, who plays Charlotte. "There are things about characters that you might've learned in the first season that pop back around, or things that you never knew that show up, or people from their pasts that pop in, so that's very interesting."

This new story- line freedom also affords the writers a chance to resurrect riskier tales they may not have told in the past. In particular, "There's some really great Cooper story lines coming up," says Paul Adelstein, who plays Cooper. "So all the juicy ones that have been sitting there that they've been waiting for a rainy day to use, I think they're loading them all up, so I'm getting a lot of good stuff to do."

As Private Practice heads into what is now a shortened season, it will do so without one original character. It was announced in May that Tim Daly would not be returning for Season 6, though how Pete leaves the series remains a mystery until the season premiere. The last we saw of him, he was on bail for the mercy-killing of his patient, and when the show returns, it's time for the trial. "It has an effect on everybody, and he is missed in ways that may surprise some of the characters," Adelstein says. Adds Strickland: "How they choose to introduce where Pete is no longer around and how it affects her world and everyone else's is really wonderful."

VIDEO: How will Pete leave Private Practice?

Despite its ups and downs, Private Practice will hit a milestone in its second outing this season, making it to 100 episodes for the series. "This is a huge deal," Walsh says. "It's very rare in television that shows make it to 100 anymore in this day and age with all the content that's out there and all the competition and cable shows. I'm really proud, very thrilled and unexpectedly emotional.

"You will, I guarantee, laugh and cry," Walsh continues. "It is deeply, deeply emotional and sad and then deeply funny."

And with Walsh's exit coming closer, she hopes the writers will keep it risky with Addison's swan song. "Either happily ever after or deeply tragic," she says.

How do you want to see Addison exit? And do you think the show should continue on without her?

Private Practice returns Tuesday at 10/9c on ABC. 

Check out what the cast has to say about this season from our set visit:

On the set with Private Practice

On the set with Private Practice |Private Practice|