They might be dead, but they may come back. Characters that had a big impulse to Dexter's personality are often making an appearance in flashbacks, visions or his... mind.
Although Harry Morgan was dead long before the pilot of Dexter, he was a huge part of the show in several flashbacks in seasons one and two, and later on as a presence inside Dex's mind.
Rita and Doakes re-appeared on the show through flashbacks in the season 5 premiere and the season 7 finale respectively. In our poll below, you can pick two dead characters you're... dying to see making an appearance in the Dexter Revival. Cast your votes!