I recently suggested something along these lines. Becoming a veterinarian is a little too on the nose for my tastes but I would be interested to know if she returned to Ludlow. Did Ludlow stay rural and a small college town? Did other people move into the Creed's old house? What happened to Rachel? I imagine her limping up Route 15 at dawn, her dark shape barely discernible to motorists, and a guy in an Orinco truck getting out to help her. As he begins to see her face and hear her voice his skin on his arms tightens and his scalp tingles, stunned in horror.
Missy Dandridge would be the only person left who Ellie might remember. Although I am curious about these things, I hope he doesn't write a sequel. It'd be too tempting to write a warmed up, reheated version of the original. (Technically, the events in Pet Sematary are essentially an endless cycle of the same story. Jud telling Louis about his dog, Spot, and the tragedy of Timmy Baterman were both events that eventually happened in a similar way to Louis and did little to discourage him from repeating previous follies.)
In regards to Doctor Sleep, King managed to write a sequel that was fresh and not a retelling of The Shining, while at the same time answering some of our pressing questions. So then, it isn't a question of King's capabilities but whether or not the story is begging to be told. Perhaps the best advice on this matter is given by Pascow to Louis: "The barrier is not meant to be crossed. The ground is sour."