Well, first we have to decide what ending we're talking about. The ending to Mau's story in which Daphne sails away and Mau goes fishing? Well, that's kind of a bummer. Sure, nothing bad happens, but—as the old guy in the concluding frame story tells us, "It's the kind of ending you get in real life" (Today.10). In other words—kind of a letdown.
So maybe the real ending actually takes place in that frame story, where we see that, even though Mau and Daphne only saw each other once more before they died, Daphne's discoveries have changed the world. We also learn that Mau and Daphne were buried together at sea.
Ironically, the old man laments that science and technology have taken over the world. It's almost as though he longs for a return to the more spiritual days of the past. When sees the dolphin jump into the air at the end, the drops of water from its tail making a shining path in the sky, "The old man smiled, and believed" (Today.79). But what, exactly, does he believe in?