Not broken up about Eflin leaving. If he wants to be a starter, go get that cash elsewhere. He might have a role in a lesser team, but he's going to struggle to catch on if his hopes is to start high leverage games for a playoff team. He's an excellent bullpen arm, and probably should seriously consider going in that direction going forward, and he could definitely be highly sought after if he's open to it (and if he was, why bail on the Phils).
Regarding the lineup for next year.... So it sounds like that Japanese player (Masataka Yoshida) is definitely going to be made available this winter. If he's serious about wanting to play here with Harper, then I'd be open to move Schwarber to DH, start the Yoshida his place, and exploring trade options for Castellanos, even if that means just giving him away. Yoshida is apparently a guy who gets on base a lot, and that could be a huge upgrade to the power bats we have. Combine that with all the benefit that eliminating the shift is going to provide to our team next year, and things should be good for us going forward.
Regarding the rotation, just grab another starter, and try to reduce, as much, the starts that Wheeler and Nola see next year to keep them fresh enough for a lengthy playoff run. They both burnt out this year and it killed us.