I don’t know if its just me but this how I see the future of these characters playing out.  
Twilight will become the new Celestia and will rule over Equestria in the future.  
Sunset will return and rule over Equestria by Twilight’s side. (Both Sunset and Luna are also ex-villains.)  
Flurry Heart will grow up to take her mom’s place within the crystal empire.  
Starlight Glimmer will become a legendary sorceress and her magical legacy will be similar to that of Starswirl’s.