Yeah, I've heard so many different versions of the ending that I feel like a lot of the details get lost in the game of telephone. But the reason I don't think it's a tragic ending is because from what I know, even though the 4HKs and Yeoryeong have their memories of her wiped, Dani manages to befriend them all again. A lot of other stuff happens in-between, but in the end, even though Jiho is the only one who really remembers Dani, they're all still friends and hang out together even in college. I feel like people often leave this bit out and just think "they all forget Dani except Jiho" with an implication that they'll never be friends again.
There's some other stuff I've read about the ending but I'm tentative on those details since I can't confirm them to be true.