Although characters certainly came and went, there was a fairly solid core cast in the original eight seasons of Dexter, but it would seem that we shouldn't expect any of them to turn up in the upcoming revival. Showtime announced last year that they be reviving Dexter for a ten-part limited-series that will see Clyde Phillips returning as showrunner and Michael C. Hall stepping back into the shoes of the serial killer with a heart of gold.
James Remar played Harry Morgan in the original series, Dexter's adoptive father. Although the character had passed away before the series even began, Remar frequently appeared in flashbacks and as a manifestation of Dexter's moral code throughout all eight seasons. While speaking to a fan on Instagram, Remar said that Showtime didn't ask any of the original cast to return, although most of them were definitely open to it.
I will not be back as Harry Morgan in Dexter season 9… They just didn't ask any of the original cast back, so I don't know what they're doing, I really have no idea. It's too bad, because all of us wanted to go back, but, you know, it's their show so they're going to do what they're going to do.
As Remar himself admits, he doesn't know what Showtime has up their sleeves with the new season of Dexter, so he's really only speaking for himself and any former co-stars he's still in touch with, but as the upcoming season does seem to be telling a brand-new story, it's possible that they won't be including any of Dexter's former associates; that said, Showtime could easily be keeping the return of any original cast members under wraps in order to keep it a surprise for fans.
In addition to Michael C. Hall, the new season of Dexter is slate to star Jamie Chung (Lovecraft Country), Julia Jones (The Mandalorian), Alano Miller (Jane the Virgin), David Magidoff (The Morning Show), and Clancy Brown (Billions) as Kurt Caldwell, who seems to be the villain of the new season. "Caldwell was born and raised in the town of Iron Lake. In fact, some consider him the unofficial mayor of their small town," reads the official description. "He’s realized the American dream by going from driving big rigs, just like his father did, to now owning several trucks and the local truck stop. Powerful, generous, loved by everyone – he’s a true man of the people. If he’s got your back, consider yourself blessed. But should you cross Kurt, or hurt anyone that he cares for… God help you." The new season of Dexter will debut on Showtime this fall.