When there is a will, there is a way.
They could pick one path, they would say it's not canon ending we are just expanding the epilogue and make a game out of it. Mia&MC's travels sounds good enough to follow, or they can even make 2 games which follows both of the options like After Summer: Mia's Road & After Summer: Sadie's Road. In Sadie's game they can even put the reunion ending too.
So in the end these things came down to 2 things, one is the business side if they expect a good revenue from it they will consider making more Mia games. The other one, which I think is the more important one, artistic side. This side includes the will of making new Mia game. People kinda miss this part but these games follow the way of creating an art. They need inspiration to write something, inspiration to crate images, they need fulfilment from creating it etc. In the end, artistic side cuts both way. When you work on something too long you'll get burned out, you won't even look at what you created, you wouldn't even want to hear anything about it and so on then after a while you'll have an urge to make some more, something new with it. So if business and artistic sides align, there is no real reason to not make another game.
All in all, I do know they said they concluded Mia story and I'd say they did it beautifully at least story-wise, I also get they busy with lots of games and they try to avoid spread too thin by starting to make another one but there is always a possibility see another Mia game down the line, maybe not soon but someday. I'll be one of the first one to buy if I see they release it.