Sorina exists because the author has given many clues and references for it. The famous phrase of Jou, that when they say it, we are introduced to Erina in the story. As a predestination. Then you can find many moments throughout the manga. One of the most recent can be found in Chapter 276, when the girls are in a sleepover, and Erina describes her ideal man / chef, and Megumi thinks that description is the same as Soma is.
One possible end is that Soma stays with x girl, and Erina with x boy. Their children are in Tootsuki and a new Yukihira / Nakiri rivalry is born. That would be a bad ending. As I said, this is not Dragon Ball or Naruto, SnS closed with low sales and low popularity. Besides that the sequels starring the children turn out to be bad.
I want a Sorina, that would be the good ending. Or leave an open end, that they are single and focused on the kitchen.