Forever Free (The Forever War, #3)

From back cover Ace paperback November 2000:

A veteran of The Forever War, William Mandella lives on the snow-covered planet set aside for his kind, supporting his family by ice-fishing and teaching physics. But now Mandella's life has become obsolete.

The denizens of Earth have evolved into a group consciousness and taken control of his new home -- keeping its independent human inhabitants alive for the sake of their diverse gene pool. But that's not how Mandella and his fellow soldiers want to exist. So, in desperation, he rallies the humans to hijack a spaceship and take to the stars, to begin humanity anew...

Then something goes wrong. The crew is forced to abandon ship -- and return home in suspended animation twenty-five years later. But the planet has aged centuries during their voyage -- and the crew wonders what new world awaits their arrival...