In a perfect world without cap and the expansion draft coming up, Buffalo does this deal in a heart beat. True starting G, solid left D prospect, and a scoring winger for a few more seasons are three things that could propel them into the playoffs starting next year.
If there's any team that could fix Kane right now, it's the Pens, Franson can replace Pouliot's production, and either goalie (likely Nilsson) could back up well.
If the Sabres could get rid of Gionta and/or Ennis's contract, this could work for Buffalo, but I'm not sure if it works cap-wise for the Pens.