In my mind, the window closes when other teams can offer deals. Because I don't think Hendry would let it get to that point, his best offer would be on the table before then. IMO, if he goes on the free market, he's gone.
Well I don't know if I want him on the Cubs, what with his injury history and the Cubs success with keeping players on the DL. But if he opts out, hopefully it'll bring down the prices of the other outfielders.