When they're old enough to work they'll be forced to interact with people who aren't their friends, and then they'll discover a new appreciation for email.
It won't go away all at once, but a scant few years after "they're" old enough to work, their friends will have been as well, and just we don't consider a company without a website to be a "real" company in this modern times, a company without a Signal/Facebook Messenger/Snapchat contact link will be seen as old and antiquated. I will mourn the loss of the federated open system we call email, and perhaps you're right - it may never go away. But the younger generation doesn't stay young forever.
I don't see this happening today and I don't see this happening tomorrow either.
The non-email world is fragmented. Signal? Facebook? Snapchat? Whatsapp? None have achieved ubiquity and their audience is constantly churning over to the next fad platform. Facebook has the best shot and there's still a huge part of the population that doesn't want their FB life to intersect with their work life.
Email is the lowest common denominator. The fact that "younger generations" (as if every 3 years is a "new generation"?) choose a different platform only reinforces the value of email as the only thing that everyone can agree on.
