There was some incredible engineering talent at Boeing in the late 40’s through the 50’s. I firmly believe the B-52 and 707 will both make the 100 year mark.
Another sad example of how we're cannibalizing the past for the moment. It's a common theme in Obama's America.
The USAF is already beginning a new bomber program. The B-52 is way too old and cannot penetrate the new and ever improving air defense networks.
http://www.dodbuzz.com/2012/02/24/afa-new-bomber-program-underway/
The Air Force also is looking into a pilot optional bomber.