I doubt Totmianina and Marinin intend to return - they're doing shows, Maxim has a child now, and besides they've achieved pretty much all there is to achieve in figure skating.
As for Xue Shen/Hongbo Zhao, I'm fairly certain that there have been reports indicating they're thinking of Vancouver 2010. She'll be 31 by then and he'll be 36, so they may not be as strong physically as some of the younger pairs. Of course, we have seen pairs skaters in their thirties getting good results in recent years (e.g. Tikhonov, the Suideks). Assuming Shen/Zhao can do it, I'd love to see them finally win the Olympic gold they deserve.