I'm repeating myself, but it is apropos. My dad basically smoked a pipe from right after breakfast to bedtime, including at work. He smoked only one pipe at a time and it only rested when he was asleep or eating. He started smoking when he was about 15 and quit cold turkey when he was about 65. He smoked nothing but Granger. He had one or two years, intermittent, when he smoked King Edward cigars instead, but then back to the pipe. He died at 89 licensed to drive without glasses.
So, from observation as a kid when I lived full-time at home, his one pipe usually lasted about two years, some a little longer. His only back-ups were one or two pipes that had already burnt out (cracked down the bowl usually) but were still smokeable, or a single cob the he smoked sometimes until its bowl cracked. So this experiment has been run before.