Injuries will sort out some of the toss ups but I see it like this.
d'Arnaud
Plawecki
Duda
Murphy
Flores
Wright
Tejada
Uribe
Johnson
Conforto
Cespedes
Granderson
Cuddyer
Lagares/Young
deGrom
Harvey
Syndergaard
Matz
Colon/Niese
Goeddel/Torres
Gilmartin
Robles
Reed
Clippard
Familia
1) If Matz is healthy, I don't see how you can leave him off the roster. This forces Alvarez off (who I think is only eligible if he's replacing an injured player - he wasn't on the 25 man roster or the DL as of the end of August 31).
2) IMO, if anyone is replacing Lagares, it's Eric Young Jr. I think they picked him up specifically so they would have a pinch running specialist for late game situations in the playoffs. His speed probably has more value than Kirk's overall game in the playoffs. At the end of the day though, I think Lagares makes the roster because they'll need him to start against Kershaw in his two potential starts. Kershaw's numbers against lefties are silly so I don't see them starting Grandy or Conforto, despite how good they've been overall.
3) If Syndergaard finishes strong, I can easily see the case for a 3 man rotation since it bolsters the pen. However, I feel like Syndergaard has tired a bit and they'll be better off going with 4 starters with deGrom being the only one to pitch twice.
I'd probably go with Matz but depending on the next 3 weeks, you could make an argument for Colon or Niese. Niese has been struggling big time and Colon has been lights out (albeit against bad teams) but their ERAs are still comparable. We'll see if Niese can bounce back, Colon can keep it up, and/or Matz can impress down the stretch.
4) The last toss up I see is Goeddel over Torres. Objectively, the pick is Goeddel but we all know things don't always get decided objectively. Torres has been pretty bad and now he's got this injury which, while supposedly minor, doesn't help his case. Goeddel has been nothing but solid. Really the only thing Torres has going for him is tenure.
Disclaimer, I haven't put a ton of thought into these points so I might be overlooking some details or even leaving off a semi major player that slipped my mind.