If the Cubs do a deal of a rental bat + bullpen arm, they can set up their roster the rest of the way fairly easily with Warren/Hammel as a alternating starter/long guy to save Jason and develop Adam's stuff.
13 hitters, 12 pitchers.
H - Contreras, Ross, Montero, Rizzo, LaStella, Baez, Russell, Zobrist, Bryant, Heward, Rental, Szczur, Fowler
P - Arrieta, Lester, Lackey, Hendricks, Hammel (starter), Warren (starter), Wood, Strop, Edwards, Nathan/Cahill, Bullpen Arm, Rondon
That would mean that off the 25 man you can look to use Soler, Almora, Grimm and easily replace them.
The best fits for what the Cubs would want are
1. Beltran/Miller or Chapman or Betances
2. Reddick/Rzepczynski or Dolittle