I literally don`t want fav characters to return, because this is what1s usually done to them: everything good in their life is demolished for the sake of creating a DRAMA to fuel the stories.
Look at Khan. He was completely fine at the end of the "Space seed". He had a nice, new planet, and his beloved crew, and a woman he loved. He had a cool job to do - create a new world. Yes is was going to be a hard job, but he was literally made for it, so the future held hope. When they took him into the movies and for the sake of drama, they literally destroyed everything good, and turned him into an evil, bitter man.
Look at Picard. He was fine at the end of TNG. He had a ship to run, and he had a brother to continue family business and family line. When they took him into the movies and for the sake of drama, they killed his brother and his nepfew. Came the next movie and for the sake of drama, they pulled out the most traumatic moment of Picards life, the Borg assimilation. They made him stew in it the whole movie and loose his **** completely. When they decided to bring him back for the series and again DRAMA. Again they`ve pulled out the traumatic theme, and made him live in his family estate, which he hated, which he ran away from, and which reminds him acutely of his loss of the family and his loneliness. They invented some new tragic theme with Romulan refugies, and leaving Star Fleet, in case that wasn`t enought drama.
Same with Riker and Diana. Of course, the dead child is what they deserved after everything, what else?
And of course, Seven. She was fine at the end of Voyager. Had returned home, had friends, a place, and a new romance (which might have led somewhere, or not, doesn`t matter). So when she showed up in STP, it was the same old story. Drama, drama, MORE DRAMA. No matter, if this trancision looks natural, or not. WHY does everything nice have to go to ****???
Why can`t SOMEONE in sequels have a break, IDK...
I guess, drama and bitter vigilante theme sells good.