In the most basic sense what a publisher is, is an institution that sells reputation and attention. Being on the cover of reputable journals for a scientist is like being on the cover of Vogue for a fashionista.
When people in India rip off scientific articles using sci-hub they don't compete with the core business model of publishers, they just want knowledge. But journals aren't really in the business of selling knowledge in the first place. Journals survive sci-hub for the same reason Harvard survives free lectures of YouTube and Hollywood survived ripped blue-rays on street-markets. Because these institutions are not in the business of selling textbooks or movies, they sell celebrities and status.
So assuming for a second that the publishing hegemon is destroyed, what will happen next? Will all the up and coming star scientists happily publish on undifferentiated internet platforms where all that matters is science? Some maybe, but my more cynical guess is that a thriving internet status economy would soon emerge that would inhabit the exact same niche that publishers have now. Because the exclusivity of publishers is not the tool they wield against the public or scientists, it's the very commodity they are selling.