I imagine the game is going to have something like 3-6 endings. I don't think any one of those endings will necessarily be the "best" ending because that will be subjective to each player. But I do think that there will be one ending that clearly has the most negative outcomes for Sophia. I think each player values different aspects and ideas of the game, so it makes sense that an ending that one player thinks is "perfect" is not for another player. But, I think we'll end up all agreeing on one ending being the worst for her.
That said, while I think having sex with Dylan will be the point of no return, I don't think it by itself will lock the player into this worst case scenario. While I personally don't think the idea is realistic, I could see L&P including an idea like the one you suggest. I believe that there will be a series of fail safes put in place toward the end of the game that will very clearly indicate that the player is making monumental decisions that will impact the ending. If Sophia decides (or doesn't have enough points) against having sex with Dylan, maybe endings 1 through 3 are still open to her. If she does have sex with Dylan, maybe those endings are locked out, but endings 4 through 6 are still available. If the player follows your idea, maybe Sophia and Dylan have sex once, and that narrows the endings down to either numbers 4 or 5. But, if you do choose to continue a relationship with Dylan, maybe then you get locked in to that 6th ending.
All of this is a bit simplistic of course. Certainly the relationships with Ellie and others will play a critical role in determining your ending. If you choose for Sophia to sleep with everyone under the sun except Dylan, I don't think Sophia gets away scott-free. And if the only person she sleeps with is Dylan, you may not get the worst possible outcome. But I do believe strongly that sex with Dylan is the number one critical hinge on which the entire game will pivot. Sophia may be able to balance Ellie, Julie, Patricia, Zach, Sam, Aiden, Morello, and Liam because the game is already locking us out with mutually exclusive storylines. But Dylan looms over everything if you haven't sent him away to boarding school.
In my scenario, I can see Sophia choosing to have sex with Dylan some time around playable day 20 (I think I mentioned this in an earlier post- I'll look for it). If she chooses yes, then I think it opens her up to finishing Aiden's last tasks. She doesn't have to accept these tasks, but she may not even get the choice unless she sleeps with Dylan because she'll need the extra filthy points. As Sophia completes Aiden's last few tasks, at some point she will have to make another decision about Dylan. If she hasn't accepted Aiden's tasks, the game may not allow the player to choose to continue with Dylan, but if the player has accepted Aiden's tasks then you can choose to continue with Dylan. Meanwhile the other storylines are continuing. This leads the game down the classic porn game path where Sophia is so unbelievably corrupted that she has lost all inhibition. By day 28, it is very possible that Sophia is carrying on some sort of sexual relationship with Ellie & Julie or Alyssa, Patricia, Dylan, Aiden(or other students), and Morello. If even half of that list is correct, that's staggering. I just don't see how you can write a compelling ending where anyone is happy in this scenario. It will be up to the player to keep Sophia's relationships in check, otherwise she risks it all.
Note- I listed Patricia, but I actually don't believe that she'll be an active sexual partner late in the game if you follow the filthiest route. I believe that Patricia, as Sophia's sister, will be the character that tries to reverse course away from the filthiest route. While Patricia is definitely a corrupting influencing, I don't think she wants to sabotage Sophia's life. If it reaches a point where Sophia is carrying on an affair with Ellie, Dylan, and others, I think Patricia will act as a narrative device to warn the player that their current path has extreme consequences.
In the end, I don't think the game is going to trick anyone into the saddest ending. You're going to need to go out of your way to ignore the warnings in order to get it.
And I agree that I think it would be cheap for a strictly Good Wife route to end with the happily ever after ending- it's too cliche.
