Arguably, novels have been superseded by series. A single fiction book today is a trial balloon. If it sells, sequels, trilogies, and more trilogies follow. Book tours. Merchandise, and a movie or TV deal may follow.
The goal today is to create a brand. The brand may survive the author, as Tom Clancy(tm) has done.
Shakespeare wrote for the box office. Dickens was serialized in newspapers. Real authors sell.
I don't think someone who labors over their darling story for a decade, self-publishes it, and only sells a dozen copies is any less a "real" author than Tom Clancy or Stephen King ... she's just not as professional. Writing to her is a work of love, a hobby, a passion.
She doesn't just sit down at the keyboard and hammer away until she has her thousand words for the day. That's what makes the professionals professional: they see writing as a job.
If you’re the author, I’d love to hear your response.
The context switches, such as they are, come with the traditional signal to most readers: the paragraph. Yet each paragraph is built in sequels (like you would a novel): action (assertion), reaction (consequence).
Paragraph by paragraph:
Assertion from title: Novels are still important.
Question: Are they really? Reflection as context.
Assertion: I fear modern media leaves me only frightened.
Contradiction: Realization -- It won't.
Assertion: Novels exist outside of the political upheaval they arise from.
Resolution: Doctor Zhivago as example of proof.
Section break (as a notice to the reader).
Assertion: Novels are an intimate communication between writer and reader.
Contradiction: "No one reads books anymore."
Assertion: People still read books.
Reflection: Orthodoxy of publishing and consumption has changed.
Assertion: The novel's purpose is to encapsulate its own world ("to be what it is").
Reflection: Anna Karenina was not the novel Tolstoy set out to write, but it was the novel he had to write because he was skilled enough to write it. The story was in control.
Resolution: Good novels matter because they exist as complete in themselves without being slaves to the social forces from which they arise.
Break
...
She continues in this form, weaving layers onto the theme, like one writes a novel. It seems to me like a clever way to write an editorial.
Toni Morrison is close to a safe bet but sadly doesn’t meet your criteria any longer.
So Pynchon seems like the clear winner. He’s the James Joyce of postmodernism so I’d be very surprised if he isn’t read in 100 years. If you want more accessible literature there is Franzen and Chabon.
I bet a sizable number of concurrent SF authors outlives 100 years.