Scorpion, Sub Zero, Raiden, Liu Kang, Johnny Cage, Kitana and Mileena are the series' most iconic kombatants, they won't be going anywhere.

watch the story mode ending. I said story mode,not arcade mode.
JC very clearly states to Cassie: "My work here is done"(in reference to his training the new generation,go back to the end of chapter 1,that's where he gives off his big speech about the new kids being,well,the next generation of heroes),not to mention that Sonya is very likely back with JC,which could mean she's also possibly out,as she will join him in his retirement(essentially,some RnR)
Curiously,none of the other parents got any such hints of retirement: Lao and Kenshi both got hints that could possibly indicate their return (Kenshi's revenge against the Red Dragon,hinted not only in story mode but also in 2 arcade mode endings) and Lao is a revenant who could still be rescued(admittedly, Chi is gone,but Tsung's potential return,as well as Raiden still being there does mean his revenant state can be possibly reverted. at the very least,his free will could return,if it hasn't already by Shinnok's "death") hinted by at least 2 arcade mode endings + Raiden in story mode (curiously however,it was after Chi's death,although,obviously,Raiden was not aware of what happened at the refugee camp,maybe a subtle dev hint? or maybe i'm looking too deeply into it)
Jax is another good example(although arcade mode endings suggest he dies again,sigh). So far,only JC and Sonya have been the only parents to get any strong hints of being retired. (Sonya makes sense,given that she's been in every game since Armageddon,she oughtta take a break some time,at least,that's my guess at the dev's reasoning)

No way Jax could ever be replaced. He was in every game since his debut (added to the PSP port of MKD). He is a staple. Kitana has also been added to every updated to every updated game she was left out of.

Characters like Kano, Sonya, Johnny, Mileena, Reptile, and Ermac have sat put once in a while, but if Kitana is in, Mileena will follow suit. Though almost everyone in this list has been in nearly every game since their debut, so I can see them sitting out in favor of other fan favorites.

I wager Predator's inclusion is why the Cyber ninjas sat out, but their return is inevitable. Aside from MKDC and X, there has been cyber ninja presence in the roster since MK3.

Scorpion and Raiden sat out a game, but inevitably made it in an updated version. Liu Kang sat out once and they got away with it, but I doubt they would ever do that again.

I definitely think they will cycle out Reptile and Ermac for Noob and Smoke.

Kenshi is pretty much a staple and I'd say Quan Chi as well, but he's most likely taking a break
Tanya barely missed the cut for MK9 and is one of the most reoccurring 3D characters, so I think she also has decent chances.

I agree wholeheartedly with every single point you made.

As much as I despise Jax, he is a staple and isn't going anywhere. Same goes for Kitana. Especially given now that they are infinitely more interesting as characters given their development in MKX.

I can see Kano, Sonya, Johnny, Mileena, Reptile and Ermac sitting out a game next round. Mileena isn't necessarily needed as a counter-point to Kitana anymore, not with the direction the story is now heading.

The cyber ninjas sitting out for Predator's inclusion (if its actually true and not just a fan theory) is still pretty shitty as MK characters should come before that of the guest but it is what it is and it's done.

Scorpion, Raiden and Liu Kang aren't ever going anywhere again, I don't think. Even the game Liu sat out of he was featured in the opening scene. They are the faces of the franchise so they won't be sitting out again, I don't think.

Reptile really needs to sit out a game so they can finally come out with something worthwhile for this character to do. It's fun seeing him every game but c'mon, give the guy something fresh.

Kenshi is most likely staying put as, arguably, the most recognizable face from the 3D era (aside from Quan Chi). Quan Chi will probably sit out a game but I honestly wouldn't put it past NRS to immediately resurrect him. As for Tanya, I haven't really touched her in the game itself but the overall reception I've seen online has been pretty favorable so her chances might be high for a return.

pretty good post,but Mileena wasn't in VS DCU and DA. not to mention the fact that,at least in the console ports,Kitana was planned to be in MK4 but got cut. Mileena wasn't planned to be in until MKG,where she was added to the roster.
So yeah,if the previous games and the story mode serve as any indication,Mileena might have a chance at returning(she can easily be resurrected by Tsung,or another of those clones) but there's a high chance she's getting replaced by Jade,at least in the main roster. Not every game Kitana was in had Mileena in as well,and they might want to try something different with the female ninjas (we never had a game with only Kitana and Jade in it) kinda like how MKX is the first game to have Reptile and Ermac as the alternate male ninjas (previously,it was mostly Reptile and Noob)