[clejack]

Instead of trying to disprove the dead Internet theory, try asking your friend about it. Ask why they believe it. Ask why it matters. Ask why it matters in the context of the real world with its real, living people. You probably won't be able to walk them back with evidence, but you might be able to walk them back by unraveling them with their own thought process.

See if you can take a walk at the park with this person and just observe the world. The Internet came to be not very long ago, the idea of allowing yourself to fall apart due to its decayed state is silly.