We will see. Manchin is up for reelection in 2012. Voting yes to overturn DADT won’t go over good in WV.
If the Democrats need his vote, they got it. If they can flip a few more Republicans, which should be as difficult as breaking an eggshell, they may let him slide. But, in the end, always look for a Democrat to behave as a Democrat. Unfortunately for us, the same holds for Republicans also.