As far as Le Tour went, Anquetil was asked if he ever thought Poulidor could win it, and he said something like "Yes... But only if I'm in it, and then he wouldn't be able to win". It was a kind of backhanded component, saying that Poupou needed Anquetil to be in the race to bring out the competitive spirit needs to win, but of course Anquetil wasn't going to take part in a tour where he thought he'd lose to Poulidor.
Indeed, that epic elbow to elbow battle in '64 up the Puy de Dome finished Anquetil as far as Le Tour went, and in his last tour (1966) he knew he couldn't win, but retired once he made sure Poulidor couldn't either. Anquetil was absent in 1965, and that was probably Poulidor's biggest chance, but Gimondi put too much time into him in the Alps (thus, perhaps, proving Anquetil's theory).
By 1967 he was at his physical peak and it only seemed a matter of time before he won... But a young Belgian lad called Eddy Merckx had other ideas.
He was still a terrific competitor, though, and carried on winning; he even appears in the film "A Sunday In Hell", riding Paris-Roubaix, still at the top level at 40 years old.
It's a sad loss, as cycling loses another of the superstars of its golden age.