It's also kinda silly to say it will never happen again when you have examples of George Brett, Robin Yount, and Cal Ripken who all played in the free agent era. Also you have Barry Larkin now and even a Jeff Bagwell, who debuted in the 90's, who will both likely finish their entire career with one team.
Edit: Less I forget Tony Gwynn, another player of free agent era, and Bagwell's teammate Craig Biggio.