I'd be far happier is Hart stayed till the end of the season, unless Jimmy has a good replacement waiting to come in as we don't have any sufficient cover atm.
People seem to think now he's leaving he'll be sticking in own goals left right and centre. Plenty of players have played for us in the past when they've known they are going. As someone said above, he'd probably be one of the most determined players to get a medal if he stayed until the summer.