The point of this season was to find out who's worth keeping. That work is not entirely done, but (assuming a free agent or two) they're not gonna keep everyone. Anyone not named Rhys is theoretically available or expendable. If they sign Machado Hernandez is probably gone, or at the very least, Crawford is (but yes, he is also an option for a 3B platoon).
But of all the players who have had poor second halves or Augusts, Hernandez is probably the least concerning. We know he was hurt, and on his worst day his OBP (.330 in August) is still the same or better than four other starters on a normal day. He is what he is and you move on from him because he's not going to get better or cheaper. But you do move on, if you want Kingery to primarily play 2B.
Truth is unless they get really aggressive (whether that means moving on from Santana or trading Herrera) next year is going to feel transitional still. Can Quinn play every day? Can Herrera bounce back? Can Williams hit well enough to compensate for his poor defense and lower OBP? If not Franco (or Kingery or Crawford) who plays 3B? Machado? Who's the starting catcher? Will they trade for a more reliable 3rd or 4th starter?
They need some 3-4 WAR players and nobody currently here looks like one (including Hoskins as a LF and Quinn because you can't assume he'll get enough games). Herrera still probably has a better chance of being one again if he can improve both his offense and defense. Hernandez is gonna fall short this year.
Some of it may fall on the front office, whatever the reason - shift, other positioning, instruction, the overall talent line-up - they have managed to make nearly every player worse defensively, even the ones who used to be acceptable or better.