I don't think he is really worried that we are going to suddenly revolt if he misses a day, since we tell him constantly that he is allowed to slow down or to sleep. I think it has become a battle of will with this story.
I think he fears that if he let's himself get into the mindset that it's not a big deal and he can just get to it later he will end up putting it off again and again until it'd become a permanent hiatus, never able to reclaim the motivation or momentum to start up again.
I think he sees exerting self discipline and forcing himself through to the end while he still has a tight grip on how he wants the story to go as the only way he can get this thing done, which he really wants to do, because he is too invested to stop now.
I don't think it's even about leaving us hanging, I think it might be the need to finish what you set out to accomplish, even if the goal doesn't make sense or matter to anyone else, to keep promises to yourself, that sort of thing. Because if you can't keep a promise to yourself and instead give up on accomplishing your goals it breaks you inside and makes you see yourself as a helpless failure with no control over your own destiny. And if you ever let yourself see yourself that way too long you believe it into reality and it becomes true and it is very difficult to break free from.
Idk, I'm entirely speculating, and could be a million miles off base, but that is sorta what i read between the lines from some of the things op has said. Alot of times these very good fics get longer and unreliable muses bail out on the authors, it is not easy to plan out and write all these scenes even when you use an existing world and an existing cast. It really can turn from a stress relief hobby into a desperate struggle for alot of different reasons.
That sort of concern or fear is not irrational or uncommon. I have seen alot of great stories that died because the author wrote themselves into corners, had life changes that prevented them from thinking the same way as before so they lost the voice of important characters, had their laptops explode and lose their outline or notes or drafts, even simple things like going back through from the beginning to do some minor editing has killed several stories i lovingly followed.
I am 100 percent confident this story will go the distance, we will have a satisfying ending not because we deserve it but just as a byproduct of who op is. I just really don't think op will ever give up, or quit, or fail to become their best self. They have shown so much self control and discipline its amazing. Alot of people today don't have the attention span or self mastery to set goals and keep striving for them, overcoming mistakes, missed deadlines, and the embarrassment of both to force a beautiful story into existence against all the odds. I honeslty find this inspiring in the same way Gurren Lagann is, even if I am mostly imagining these things and have it all backwards.
Don't belive in me, or the op I believe in, belive in the op who believes in themself.