Dude I bought the Swm and I'm gonna buy Returning to Mia the second they release, waiting on my wishlist. I know for a fact, whatever they release with Mia, I'll buy it. So whatever is okay for me for swm3 as long as we have Mia. I also do want to see more of her too but I do understand when creators, especially writers, get sick of what they are creating it's better to not continue because from that point it just downhill.
My hope is, after a year or so they want to make another Mia game by themselves without getting forced by the fans so game can keep its quality.
To answer your question, here's a few thoughts off the top of my head;
- MC and Mia move in together where MC studies.
- MC and Mia move to a country they can get marry and open a little cute café together.
- MC and Mia decide to travel together, so we see their road trip adventures. Every chapter new people, new places, new experiences.
- MC and Mia manage to hide their relationship from everyone. MC breaks up with Vivian's bitch and Mia from her imaginary boyfriend. They have long distance relationship, MC trying to be faithful etc. and next year's summer Mia would come to visit MC. Mia meeting with MC's friends, getting used to MC's neighborhood, maybe a Summer job, also aunt, mother, Isla, Cindy etc. could visit them time to time. If MC could not manage to keep it in his pants, it could come and bite him the ass when Mia is there with him. Also Vivian's bitch could be the main antagonist of the game. She would not know what's going on between MC and Mia, but she is suspicious about it. So while trying to win back MC, she could dig around to get rid of Mia once and for all. After all, iirc she said she wasn't going down without a fight. Her success could be related to how loyal MC to Mia throughout game and ending would be hardcoded. Like if he was loyal enough, or clever enough in his escapades, they will get happily ever after ending; if not Mia would break up with him eternally this time. Also Emma could be the anti-hero of the story, helping MC and Mia from shadows with her deranged ways.
So, if you think about it there is always a way to keep the story alive. After all, movies and games bring dead people from their graves to keep their story go on but if the writers don't want it, don't desire to write anymore even the best stories would go south. All in all, it's their game and it's their decision.