His readers (not audience) paid to buy the books he had written. They didn't pay him to write books in the future. I really don't understand this bizarre "fandom" idea that a writer owes his readers something beyond what they have paid for. It's a polite fiction that some writers unfortunately indulge, but the fact that you've paid a small amount of money to read a book doesn't impose any future obligation on its author.

His publishers might have cause to be annoyed if they have a contract for more books, but the readers, however disappointed, don't have a moral right to dictate a writer's future labour. And that's what writing novels is—it's work for money, like programming or plumbing, not some mystical calling or vocation.