It’s been a long, long time since I watched the original series (haven’t even bothered with the spin-offs); but my vague memory was that all they needed to do to end the show in a way that appealed to fans was to:

Have a largely shot-for-shot recreation of the introduction with an older Dexter, set in Argentina, and ending with him seeing Hannah and the kids having breakfast at a cafe and ending with a knowing smile at the camera.

Like to say, hey - new location, still the same ol’ Dexter.