The ending could just be that Sophia has a choice to make, either she stays with Liam or she leaves him.
Whether or not she ends up alone or with somebody else is some what limited
That would be too straightforward and boring. Honestly if that is a choice given to us irrespective of how many Filthy points we have or the acts that Sophia has committed throughout the game then what was the point of playing all through this.
I would like the Endings to not even gives us such a definitive choice. Like the Endings should be distributed based on the points we have and not give us any explicit Choices.
Suppose Sophia has
Less than 250 filthy points till the end - she can have a good ending.
More than 250 but less than 350 - both the bad and good ending can be made available and the player decides.
More than 350 - Bad ending, the player has no choice but to take the bad end.
Personally I would also want like a redemption choice. Where you see Sophia comes to terms with reality. Accept all her mistakes, regret the bizarre things she has done and ask Liam to forgive her and is given a chance to make things right. To leave this in the past and have a new beginning. Considering this as phase in her life that provided her with an experience ( both good and bad ) that she will never forget.