Unlike the Pubbies, the Dem’s don’t seem to be wedded to the “their turn” theory of nomination. If she starts to look like another Dole or McCain they’ll throw her under the bus.
Main drawback IMO is that she looks hideous in HD. And she becomes extremely shrill if someone manages to get under her skin. And by the time 2016 rolls around many in the electorate will have no memory of her husband’s Presidency.