Update: Bungie community manager Cozmo hit up Reddit yesterday to say that an official Music of the Spheres release is "coming soon." Interestingly, it appears that nobody bothered to mention that fact to O'Donnell, although given that it was "work for hire," as he previously described it, that's not entirely surprising.
The same thread also contains what could be taken as a hint that Bungie is at least open to the idea of mending fences: Responding to O'Donnell's inquiry, Destiny 2 game director Christopher Barrett wrote, "Some hope for the future, some wait for the call." That's the opening line to Paul McCartney's 2014 Destiny song, "Hope for the Future," which despite being thoroughly awful is also relentlessly optimistic about what lies ahead.
Music of the Spheres was intended to be a "musical companion piece" for the original Destiny, co-created by Marty O'Donnell, Michael Salvatori, and Paul McCartney. (Yes, that Paul McCartney.) But because of an acrimonious legal dispute between Bungie and O'Donnell, who was the composer at Bungie from 1999 until his ousting in 2014, it was never released. And it still isn't—but thanks to the efforts of an unknown leaker, you can now get your hands on it anyway.
The album can be heard on Soundcloud, embedded above, or downloaded (check this Reddit post for current links) for offline listening. The links may not last for long because it's an entirely unsanctioned release, but Joseph Staten, who served as writer and creative director on multiple Halo games prior to joining Microsoft Game Studios in 2014, was clearly pleased with the leak.
One of my fondest #Destiny memories was writing a thematic summary of the game for @MartyTheElder that he gave to @PaulMcCartney. Not every day something you write (“Hope shines brightest in the dark”) ends up being sung by a Beatle. Glad #MOTS is finally out for all to hear.December 26, 2017
So was O'Donnell, who told Kotaku that he's "relieved and happy" that the music can finally be heard.
"My wife and I spent the afternoon with my now 93 year old father and we showed him that people were finally able to hear this work. It made our Christmas even better," he said. "My mother, his wife of over 60 years, died a couple years ago and although she loved listening and shared it with some of her friends (she was a musician) she never understood why it wasn’t released."
"I don’t know who actually did it but they have my blessing. I honestly don’t know how anyone could begrudge this any longer."
In fact, O'Donnell made it clear in November that the music was already out there somewhere, and he wouldn't mind at all if it ended up in more hands.
Years ago, when I was Audio Director at Bungie, I gave away nearly 100 copies of Music of the Spheres.I don't have the authority to give you permission to share MotS.However, no one in the world can prevent me from giving you my blessing.#NeverForgetMotSNovember 30, 2017
He also said that he has no financial stake in the matter either way, because Music of the Spheres was "work for hire" and he's already been paid for it. Neither, as far as he knows, does Destiny 2 publisher Activision, which as far as he knows doesn't own the Destiny IP. That might reduce the possibility of legal action forcing the album offline, although Bungie may still opt to go after it: According to Gamasutra, it was awarded the rights to the album as part of the settlement between in and O'Donnell.
Music of the Spheres includes an extended mix of Hope For the Future, the Destiny closing credits song performed by Paul McCartney that Staten mentioned above. It's a bit of a bombastic mess (so I think, anyway, although a lot of people seem to like it for some reason), but it's the video that really puts it over the top.