Isn't there a confusion here when you're saying that novels do something that no other medium can do? Some kind of category error or something.I guess I tend to think about these things ("can there still be a novel in the age of the web?!") in terms of ecological niches, and what things provide that other media don't. Visual arts are in a real crisis now cuz photography set somethin off a century ago, and books are in a similar place with movies and TV. If you want immersive narrative form—traditionally the bread and butter of novels—a screen's an easier, smoother experience.
But I think the one things novels can still do that no other medium can touch yet is something like "psychic occupation"—the ability to get inside a consciousness. That's why in my mind it's no surprise authors like Knausgaard and Ben Lerner and Maggie Nelson are such constant presences.
What I mean is, if a novel is written on the internet is it a novel or not? Is the medium "novel" or is it "internet" or is it "book" (meaning on paper in a thing you hold)? Cos from what you're saying above if you took a novel and just wrote it on the internet surely its medium has changed from book to net but it hasn't stopped being a novel has it? I don't know that it's wrong to use the word medium for any of those things - but there appears to be some difference between the way you are using it in each case, perhaps they are media in different ways or something and I don't think what you're saying above captures that somehow. Does what I'm saying make sense? I'm not sure I'm explaining it properly but I do think there is an issue there even so.
Separately but relatedly if Knausgaard wrote his next novel on the internet - but straightforwardly as a novel, using no tricks, just wrote it as it would be on the page, then surely it could perform the "psychic occupation" that you refer to in the same way. So the internet can do that. Of course it's kind of a cheat to restrict the internet to what is available to the novel, but the very fact the novel can be contained within the internet in that way means that it can't be true that there is anything the novel can do that the internet can't.
So suppose Knausgaard wrote his next novel entirely as pages on the internet and it was a good novel and it achieved the psychic occupation you refer to above, ok, all cool. But suppose he added one single thing that is not possible in a book - a hyperlink or a moving picture or whatever - does that mean the psychic occupation is automatically destroyed? I'd say not, in fact I'd argue that, with skill, he could maintain that and add something extra... and what if two hyperlinks, or three? To me it's not inevitable that there should come a point where anything is lost and it's entirely possible that something could be added.
To anticipate one possible argument against that last point; maybe - counterintuitively - it's not true to say that you can just include a book within internet - you would think that you could include theatre inside television or film by just filming a play but that doesn't quite work and the play does look wrong and lose something (nb I'm not saying that you can't can't make a good film out of a play, I'm saying just putting a still camera filming a play and filming it precisely as it is will not recreate the play with the same feel as you would have if you saw it actually live). But I reckon you can.