If my memory does not fail me, the book COmmand Control claims that it did continue until well in the 90s.
> Speaking of heartless and barbaric, Schlosser covers Richard Nixon’s “madman theory,” which he and his close adviser Henry Kissinger developed after Nixon took over the presidency in 1969...
> How to show the world he was a “madman”? Nixon and Kissinger came up with a plan in 1969. They ordered the Strategic Air Command to go on airborne alert for two weeks. “Ignoring the safety risks,” Schlosser notes, “B-52s loaded with hydrogen bombs took off from bases in the United States and flew circular routes along the coast of the Soviet Union. Neither the Soviets nor the Vietcong was fooled by the bluff.”
https://vva.org/arts-of-war/history/command-and-control-by-e...
That occurred after the Thule airbase accident that prompted the end of continuous air alert in 1969.
"The airborne alert program was terminated the day after the Thule accident. The risks no longer seemed justifiable, and many B-52s were now being used to bomb Vietnam."
The Thule accident was, of course, in 1968.
I don't recall there being anything else about a continuous alert being resumed afterwards, but I certainly could have forgotten.
Edit: since we're talking about this book, if anyone is interested in stuff I highly recommend it. The full title is Command and Control: Nuclear Weapons, the Damascus Accident, and the Illusion of Safety by Eric Schlosser. Available wherever fine books blah de blah blah.
I'm sure it could be restarted now if it looked to be necessary, but it doesn't seem to be.