I, for one, thought this was a pretty competent way to wrap up the story. I'm used to way worse from less competent authors.
The Owl Tribe's laziness in finding solutions led them to further rely on Kara, who, fearing Vivi only saw her as a friend, reluctantly resigned herself to her fate. Kara, after Vivi confessed that she is starting to love her that way, stood up for herself against her "duty" to the Owl Tribe. After Kara (temporarily) turns down Rumilu, he, already peeved by having his desires disregarded by the elders, agreed to find alternative solutions. Importantly, these alternative solutions are twofold, they don't have to both find titans on earth and unify the titan tribes for Kara to be left alone (because, remember, the problem here is the Owl Tribe's low population, not the entire species.)
So here's their likely futures:
1: Kara and Vivi convince the canyon titans to agree to join the Owl Tribe and repopulate it. Yuri lives.
2: Kara and Vivi can't convince canyon titans to join the Owl Tribe, and Rumilu successfully unites the remaining tribes (that most likely have women in them). Rumilu no longer needs to bother the couple. Yuri lives.
3: Kara and Vivi can't convince canyon titans to join the Owl Tribe, and Rumilu can't unite the remaining tribes. Rumilu, having already denied his elders and not wanting to further rely on Kara, continues to find other solutions out of respect. Or maybe he just leaves the tribe to be lazy and wither away. Yuri lives.
This is a Neji story. Vivi isn't going to be demoted to the queen's extra special friend while Kara is forced to pop out kids like a broodmother. Neji's stories can have tragic endings, but they're not that tragic.
I liked the "Im not sure if my love is the same as ur love" trope here, too. If you look at it from the lens of Vivi wanting to return Kara's feelings, it makes sense she would slow down the relationship until she can fully recognize and return her love. She had some deep trauma surrounding accepting love, so expecting her to jump straight into Kara's arms and make out after she accepts it ignores the juicy opportunity for some sappy sapphic healing. There's no doubt they'll grow into each other.
Or maybe it's a 20 chapter webcomic and I'm reading too deep.
Regardless, I feel like I got the giant x vampire yuri I wanted. Solid 6/10.