Arrow producer Marc Guggenheim explains why he believes Oliver Queen got a happy ending. As the titular Green Arrow, Oliver's journey over the course of eight seasons had its highs and lows. In the course of protecting his city, he became very used to sacrifice, losing many of his family members and friends. His own death was heavily foreshadowed throughout Arrow's final season, leading up to the massive Crisis on Infinite Earths crossover. Ultimately, Oliver sacrificed himself to save the universe, not once but twice, as he did the same thing after returning as the Spectre.
Though death is not what one would think of as a traditionally happy ending for a beloved character, Oliver's sacrifice did have a silver lining. At the end of the Arrow series finale, his wife, Felicity Smoak, joins him in their version of the afterlife, implying they spend eternity together. Understandably, some fans were disappointed by this turn of events, even though it was widely believed Oliver would die during Crisis on Infinite Earths. Recently, Guggenheim commented on the conclusion to Oliver's story, perhaps making some fans feel better about it in the process.
Appearing on Literary Joe's Inner Child Podcast, the producer acknowledged that some fans were disappointed by Oliver's ending but explained why he believes it's still a happy one, at least in the world of Arrow:
I know there's a lot of fans who really feel Oliver deserved a happy ending, and I will say, for my money, I feel like we gave him the Arrow version of one. Arrow's always been a really dark show. I think the show has sort of thrived in its darkness, and I think that's one of the reasons why the idea that he would get a traditional happy ending where he gets to ride off into the sunset with his wife and his daughter, it felt incongruous with the overall tone of the show.
Guggenheim makes a good point, especially about the tone of the show. Even those upset by the series finale have to admit it fit in well with the rest of the series, during which several beloved characters died. In fact, essentially everyone important to Oliver at the start of the series, aside from his sister, Thea, is dead at this point, or at least was in the timeline before Oliver's death. Viewers were also heavily clued into the fact Oliver would likely die during Crisis, which should have lessened the sting a bit. In that regard, the end of his story was much happier than it could have been. The afterlife tag is what makes the difference. In a way, he does "ride off into the sunset" with Felicity at least, though their kids remain on Earth.
Guggenheim's comments about Oliver's ending being happy in the world of Arrow specifically raises some questions about what the finales of other Arrowverse shows could look like. By this logic, it seems unlikely The Flash, Supergirl, or Legends of Tomorrow would similarly end with the death of their heroes, as those shows are generally lighter in tone. Batwoman, however, hews closer to Arrow in that regard. Though, it's hard to know at this point if the finales of other Arrowverse series will make Arrow's seem better or worse in hindsight.