I read Kyoshi's attraction towards Yun as simply a crush, mainly brought about by Yun's excessive flirting and obvious interest in her.

The novel seems to suggest that the interactions between Kyoshi and Yun usually revolve around those lines. It is also noted that Kyoshi didn't believe that it would be possible to pursue her attraction towards Yun. Though it is interesting to consider how these sentiments that Kyoshi once had for Yun seemed to prevent her from accepting that Yun had changed for the worse.

There was also that moment in Tagaka's camp where they slept beside each other and Kyoshi didn't want to move away from Rangi even though her arm was already sore.

The chapter titled "The Iceberg" seems to be a defining moment in the attraction between Kyoshi and Rangi, it is a major point in their relationship. It seems to come up right after the novel explores the dynamic between Kyoshi and Yun. The level of intimacy and trust within the scene surpasses that of any interaction Kyoshi and Yun had, Kyoshi's pleasure in comforting Rangi during this scene is established as well.

she literally revealed herself as the Avatar by singing a poem that made her think of Rangi

It seems to be a rather vague moment as it seems to have been something she launched into without thinking. However it does foreshadow the extent to which Kyoshi cares for Rangi, as shown in a scene in "The Iceberg".

It is interesting to note that Kyoshi's perceptions of Rangi and Yun are introduced in the chapter "Nine Years Later". The novel seems to focus on Kyoshi's dynamic with Yun in the chapters "Promises" and "Desperate Measures". The novel seems to focus on Kyoshi's dynamic with Rangi in the chapters titled "The Iceberg" and "The Fracture". It seems to switch between these two characters up until the chapter titled "The Spirit" where Yun is effectively eliminated.

Then the novel expands upon the dynamic between Kyoshi and Rangi from the chapter titled "The Inheritance" to "The Introduction", as Kyoshi and Rangi comfort each other during these times. The novel then deepens their relationship in the chapters titled "Escape" and "The Agreement", as Kyoshi views Rangi in a far more positive light and Rangi treats Kyoshi with more discipline, a sign of affection. Then the novel firmly establishes their romantic relationship in the chapter titled "The Town" with the deep conversation Kyoshi and Rangi have nearby a lake.

So whether or not Yun died, Kyoshi would still have ended up with Rangi one way or another.

It is the most likely outcome.