Like do we know for absolutely sure that it ends happily? I'll be a bit peeved if it does because a sad ending would have worked. Having the Champions fall would make for a really strong ending.
If it does end happily that's still cool though. I honestly don't like the bait Nintendo used as it's marketing though. It's being billed as a "prequel" and sure... they haven't outright called it that, but nothing in the trailers, or marketing has indicated that this is an alternate take on the war 100 years prior to BotW. If they just billed it as such by showing off Riju, and Teba and stuff then yeah, it would be a lot more honest, and the game would STILL sell quite well. Instead they've been purposefully misleading with the marketing.
That's... concerning. You can argue technicalities all you want about Nintendo never coming out and saying it's not a "prequel" to BotW... but they've been purposefully vague about it's purpose as a game, and that is frustrating. Nobody from the marketing team, or the Treehouse has made mention of it not exactly being a prequel so much as a reimagining of the events leading up to BotW. Instead they've teased ONLY the 4 original champions, and made nods to events that happened in BotW's version of history. The only outright clue that it's not a direct prequel we've gotten is the time-traveling R2D2. Which fine, but being purposefully misleading is a bit screwy imo.
All that said I plan to play it anyways, because I love BotW's world, atmosphere and lore. It's a cool concept to depict the war prior to BotW that left Hyrule in ruins, even if it's just a fan-fic version of the story. That said I wonder how they're going to implement Teba, and Sidon and stuff... that's going to be some... Fire Emblem Awakening level ugh if done wrong.