The story reached its natural conclusion.
There is nothing more that needs to be told, and I don't think that additional chapters
(apart from the following epilogue) are necessary at all.
- Mizu'umi, thanks to the letters, found out that none of what happened to Sora was her fault and that, just as precious as Sora was to her, so was she herself to Sora.
- Renju found something in life he really enjoys, no matter how hard or stress-inducing it sometimes is.
- Even Himawari technically found a way to help Sora. She not only encouraged the duo to continue, but also was the one who made Sora's aunt hand over the letters. Her career also stopped stagnating and is back to flourishing once again.
And now, even after the time-skip, Polaris is an idol group that's remembered rather fondly, partially thanks to all the mystique surrounding it. Everything that was Sora and the Polaris she created was, and still is, influencing the people to this day, even if only by a little.
And so you can, with certainty, say that
Polaris Will Never Be Gone.