You guys know darn well the 1911's reign ended the day they first issued the M9. That would be 1985. The 1911A1 was adopted in 1924, for a total of 61 years service. The M9 has been in service for 26 years. Therefore the M9 needs 35 more years to tie.
The M1911 was adopted in 1911, and slightly modified in 1924 with the A1 provisions. However, you can't discount those first 13 years of service simply because the gun didn't have the arched mainspring housing or the shorter trigger. The gun was the official sidearm of the US for 75 years.
As far as the M9 outlasting it, I highly doubt that. The Aluminum framed M9's do not have the same longevity as the steel framed M1911. Instead of constantly replacing worn out guns I believe the military is more likely to adopt something else, likely one of the popular striker fired polymer designs.