Unstopped by any hospital personnel or security, Dexter wheels Deb through the hospital and outside. He covers her with a sheet (might have done that earlier), picks her up, and takes her onto the boat. As contemplatively mournful musical cues play, he drives out a good distance from shore and then stops, pulls out his phone, and calls Hannah. In contrast to the storm around him, Hannah and Harrison are in sunny Jacksonville, and she excitedly tells him they're going to make it. He says he's still in Miami but will be leaving soon, and she excitedly talks about the length of the Argentina coastline and how they can keep going until they find the perfect spot. Then Hannah puts Harrison on so Dexter can tell him how he wants him to remember "every single day" that he loves him, and Harrison's like, "Awesome, later!" Then Dexter chucks his phone into the ocean.
With the sky now pretty black in spots, he unveils Deb and caresses her face before picking her up and dropping her overboard. What a dick! There are people who actually cared about Deb; you're going to deny them a funeral and keep them up at night wondering what happened to her? This finale has shown more than anything else that Dexter is a selfish, weak man who's skated by on luck and the kindness/stupidity of other people. He got off scot-free from the LaGuerta investigation, the only thing that's ever really threatened to bring him a day of reckoning, and now he's going to abandon his son and the woman who loves him because he's having FEELINGS that will probably pass within a day anyway, if history is any indication. Speaking of which, DVO boo-hoos that he destroys everyone he loves, and he can't let that happen to Hannah and Harrison. "I have to protect them…from me." He starts the boat again and drives straight into the storm.
Then we cut to a Miami bathed in sun yet again with news-broadcast VOs letting us know that Hurricane Laura (that was Dexter's mother's name, right? Sure the writers thought that was clever for some reason) has passed. Out on the water, the Coast Guard finds the wreckage from the Slice Of Life with no apparent survivors, and then we see Batista get a call informing him of the news. In Buenos Aires, Hannah and Harrison are at a little café when she sees on her iPad equivalent a story about Dexter apparently having been lost at sea; she looks overwhelmed, but keeps it together for Harrison's sake and leads him off to get some ice cream.