I would not assume that a new generation will definitely take over in 2016. Assuming that VP Joe Biden takes a pass, Clinton would come into the race with a resume -- First Lady, senator and secretary of state -- which would stand out against other governors and senators in the race. It is also possible that President Obama might endorse her, which would carry major weight.
Yes. Gore, Dole, Bush sr, Nixon were all fairly prominent politicans 8 years before they got their party's nomination and all of them had ran for the presidency previously. There is really no reason to assume we will have all new faces in 2016.