For some perspective, the Boeing 747 first entered service 50 years ago and no American carrier operates them in passenger service anymore. Nothing lasts forever.
But 462 newer versions (339 747-400s and 123 747-8s) are still in service with several foreign airlines, such as Lufthansa and British Air. I flew on one in September, but I prefer the Airbus 330 and 340, along with 777s and 787s