The Clinton's are their own brand at this point.I have very little confidence that 4 more years of Obama will put the DEMs in the public's favorable graces.
If things keep going down the shitter, it actually only strengthens their brand politically, and increases the likelihood Hillary could be President.
Clinton nostalgia in this country has only grown since for many people (how bizarre is this) it represents the last time America was booming and the economy was expanding (not the jobless recovery type expansion we had all last decade).
I could quite easily see them (Bill and Hillary are a team at this point) campaigning on the idea that you need to put them back in charge to get the country back to where it was when they were last in charge.
I am not taking into account any of the variables that led to the prosperity then, but from a strictly political point of view it is a very powerful argument and would be tough to really assaile running against them.
The Clinton brand has staked out a middle ground centerist type brand. Hillary will run on Obama having veered too far left, the Republicans are too far to the right, and that the Clinton brand of centerist governance is what will bring America back to prosperity.
I can just see it now, and I am sure the wheels are in motion for her to take the next 2 years off to recharge the batteries to gear up for a 2016 run. She is not the pariah she was 4 years ago (losing to Obama humbled her tremendously in the eyes of public opinion). her favorables are really really high, and Bill's are through the roof. She will only be 68 during the next campaign, so while on the outside bounds age wise it isn't the deal breaker it would be if she was in her 70's.