When you go to the federal pen, you serve the time you receive, unlike state pens where you can parole out after serving a certain portion of your sentence, anywhere from 1/6th to 3/4 of your time, depending on which state you are in. So Bernie is SOL and will die in prison unless he is pardoned by a future president (and no I won't open that Pandora's box)
As far as the 2.5 mil Mrs. Bernie is keeping, I thought I read where that money could not be tied in any way to the Ponzi scheme and that was why she got to keep it, at least temporarily.