Seriously, we will go with a 4 man rotation in the playoffs. The only way Lannan starts in the playoffs is if Davey thinks there is an advantage to slipping Det into the bullpen as the go-to shut down guy in the middle innings. That is a remote possibility but mimght be the cagey thing to do.
Lannan will have a problem making the roster in the playoffs. He'd basically have to move ahead of Gorz and Duke as the long releif lefty. The other two have been effective in that role, while Lannan really has not pitched relief.
Assuming a 4 man rotation of Gio, JZ, Det, and Jackson (righties 1 & 3 if vs. St Louis, lefties 1 & 3 if vs. ATL), we will go with a 7 or 8 man bullpen. Righties will be Storen, Clippard, Mattheus, Stammen, and probably Garcia. Lefties will Burnett, M. Gonzalez, and one of Gorz / Duke / Lannan. Lannan might not be the best option. The cagey way to play it, were we to face ATL, might be to have Lannan start game 3, Det in the bullpen as a 4th lefty and drop Mattheus. that lets you use M. gonzalez as a LOOGY.