A 20,000-word plot isn't exactly long, but it isn't short either; in fact, it wouldn't be a big problem if he didn't revise it.
He could gradually correct it in the subsequent plot.
By doing so, he could ensure a consistent update schedule and not lose the existing readers.
But...
If he didn't make changes, no matter how much he adjusted those 20,000 words, they'd never be as good as the plot he had initially planned, and they would become the downfall of the book.
If he didn't revise, he might still be able to aim for an average of 3,000 subscriptions for a fine work, but if he wanted the book's performance to continue to climb and become an author like the ones who wrote "Ice and Fire Six Realms," that would be very difficult.
It all depended on whether he was satisfied with the current state or willing to take a risk.
