Okay, now that I'm actually rested and a bit more sane (relatively speaking), further theorizing on the next update. Option 1 (sex with Yumi with a monkey's paw) and Option 2 (we find out the content in the letter Nodoka wrote to herself/we find out what was buried beneath our feet) are still on the table.
Actual Option 3: Chinami dies. Her illness is set up early in Chapter 1, we had some foreshadowing in chapter 3 with a muffled cough within her dog mask, and the turnaround time between a foreshadow and the event playing out is about one year (Maya foreshadowed her own reset at the end of chapter 2, poofed at the end of chapter 3). This would absolutely break multiple characters beyond just Chika and Yumi, as she's become very close to the Tsukiokas. Her illness is also a Chekov's gun that becomes increasingly wasted if it ISN'T brought up in a narrative-relevant way for too long. So her dyiing -- and appearing to stay dead for at least one cycle before returning -- needs to happen eventually. Or perhaps she dies and becomes Something Different (tm), as the game has shown that death is sometimes merely a transition (Sekai).
That fact that "Chinami is likely to die" in a world where death within the narrative is portrayed as temporary (Bluejay) is an odd intersection, and at some point we need to find out exactly what that looks like.
Finally -- in her first appearance, Sensei calls her an angel -- a word that has become inreasingly loaded as the story's progressed.
I think this is the most likely option, honestly. Plus, this is a narrative opportunity to pile on Chika's misery, which is a thing this game loves to do.