This article seems to suggest it's possible.

"Analysis: Could Clinton land the VP nomination?"

And for what it's worth - The other night in Memphis I had dinner with one of the leading political pundits. This fellow is known as non-partisan and appears on the Sunday morning and other political interview shows, was recently interviewed by Charlie Rose. He himself has interviewed all the candidates over the course of the primaries, some several times. As well as being a columnist for a national magazine he has a closely-held newsletter which analyzes political races for the RNC, DNC, etc. It was a rather small dinner, 7 people, and I had a chance to ask a few questions. (I was an accidental guest. The guy is the brother-in-law of a friend from home who was in Memphis to attend a family celebration, and the pundit was there for the same celebration. Since I was in the neighborhood I swung by.)

I asked him if Clinton would be the VP nominee, and he said definitely not unless there are unforeseen developments. I then asked if the Clintons would soldier on with Obama or take their marbles and go home. He thought they would be good soldiers and stay positively involved with the Democratic Party.

I also asked why the Sunday morning and other political TV hosts would ask a question, the guest would launch into a speech with little if any bearing on the question and the host wouldn't bring the guest back to the question. The guest would make a speech on his or her own topic and leave. He said it was because if the host were known as tough the guests wouldn't come back and they didn't want to "make news". Russert, he said, could be the toughest because his program has the highest ratings.

As I said, that's for what it's worth.

Arf