If Clinton gets the nomination and loses in 2008, then Obama is the frontrunner for the Dem. nomination in 2012. After not running in 2004 or 2008, I don't think Gore is likely to run for president ever again.
Incidentally, when was the last time someone was out of public office for 12 years or more, and then made a serious run at their party's presidential nomination? Has it happened at all in the last few decades?
Well Nixon did it after 8 (1960 and 1968) but I can't think of anyone who did it after 12.