We will not go after him, if he is indeed in Iran. I find it odd though that he's in Iran. He certainly would be a pretty nice chip to have in your pocket for a possible play. Iran could use him to negotiate the US to back off their nuclear program (very unlikely we would go for it though).If you're Iran then having a wanted terrorist taking up residence in your borders would add a yet another reason for further sanctions and possible military action if was thought to be likely he was indeed being harbored there. If I were Bin Laden I'm not sure I would want to be in that position but then again there are huge risks for him no matter where he goes.
I'm curious to know what our intel people think about this possibility, if they do know would we choose to make it public since we are obviously trying to appease them in some fashion and get them to the table to negotiate. If it were found to be credible and likely true he was in Iran it would throw yet another kink in the issue and open Obama to even further backlash here at home. It would certainly create a new problem to deal with.