Pallister still thinks the Manchester United boss will be around for a few years yet to continue the remarkable success of his first 25 years.
But Pally, signed by Fergie in 1989, said: "Obviously you have to look at who can take over, although he would seem to be irreplaceable. He is still as feisty and as passionate as he was, that's for sure.
"Sir Alex is almost 70, but it beggars belief that he's stayed at a club like United, with its huge expectations, for a quarter of a century. It's unheard of."