I'm just going to ignore all the talk about piracy, because we've discussed this multiple times already and I prefer to talk about the game itself on its forum.
I highly doubt she's going to get more years.
Even if there were treatment, it would probably be expensive, far out of Yumi's and Chika's reach. Their only hope would be the Tsuiokas. Maybe fellow 5000 year old wizards will get along and everything will be fine. They will run Chinami Corp. together and ride off into the sunset on giraffes.
As for getting erased:
Well, Chinami dying would certainly be a easy way to drive Chika and Yumi over the edge (or over the place where the sidewalk ends, ha ha, reference). That said it would be likely for her to be like Makoto and just reset to a slightly altered previous state.
Unless main characters and side characters differ in more than just game mechanic/focus.
As do I.
The thing is, we don't know exactly what she has, so we don't have any way of knowing how much time she has. This opens up quite a few possibilities not only on her line of events, but Chika's, Yumi's, and even Rin's given that they are friends. It could be something like they find something to help or even cure her, although I doubt this very much on the genre of the game alone not to mention we do know what type of issue Chinami has, a type which are rarely curable, leaving the afflicted to AT LEAST be quarantined for life. In real life, the Vtuber Ironmouse is one such person and is under this restriction, which is where I got that info. It could also, and will more likely, be something tragic. She could be one of the first deaths in the game if they do occur and it could become something tragic spanning several lines of character events, especially the ones I listed.
As for treatment, issues like hers typically are very expensive, that's why quarantine for life is one of the few options other than just letting themselves fall victim to the effects. Even someone with a simple cold is life threatening to people like Chinami or, in real life, Ironmouse. Issues like this often involve expensive drugs or even more expensive and highly dangerous experimental treatments that could kill them outright. This would most definitely sink Chika into an immense debt she would likely never pay off, Chinami would likely still not be safe from her issue, and the source of that debt likely wouldn't be from some reputable source given the amount she would have to borrow, but someone extremely shady like a loan shark, who might even make her do some very bad things as punishment for inevitably missing payments, the kind that the side content of the game is all about. Even with Yumi's help in trying to discourage such things, she may be forced into it.
Chinami dying could very easily be the final push Chika and Yumi need to break, you're right. I really don't want to see them snap, but it is likely inevitable.