J.D. Martinez is out for the year after he has surgery to remove part of his hamate bone removed on Wednesday. He'll be out for 4-6 weeks, and the Astros are hopeful he can still play Winter Ball.
Pablo Sandoval is the player who comes to mind when thinking about returning from hamate bone surgery. Telvin Nash and Rafael Valenzuela had part of their hamate bones removed in the 2011 season.
Here's a Baltimore Sun article on the recovery process.