In the pen you for sure have Maton, Miller, Palencia, and Rolison back. Ethan Roberts is also available for the Iowa shuttle along with Assad. Definitely need another impact arm there but I suspect Morejon will be high on many team's lists.
For the rotation, you're looking at Cabrera as the only highly likely candidate to give you 25-30 starts who's currently on the roster. I think I'd probably make an effort to bring back Peterson in concert with a dogged pursuit of Skubal. They just don't have anyone who can be a top of the rotation guy anywhere near MLB ready and maybe not even in the system at all. I kind of hope the clunky end to the season for Holmes leads to him exercising his option and you add him to the mix with Steele, Garrett, and Brown filling out the rest of the staff. I'd also look at Civale in the Rea role for 2027 if not a straight pen role since he's obviously figured something out since coming to the Cubs.
I probably try to bring Kelly back and have him work at 1B in the offseason as a platoon partner with Busch so you can break in Ayers without having to worry about a 3rd catcher really screwing up the roster. I'm making a QO to Seiya for sure and probably Happ depending on how that discussion goes. Assume Happ is back, Alcantara is his platoon partner, and I'm not sure what you do at the other OF position. Maybe a buy low Jarren Duran trade or something like that? That leaves you a bench of Pedro, Shaw, Ayers, and Amaya with one of the first 3 hanging out in Iowa to start the season so the roster fits the Happ/Alcantara platoon.