I've heard 2 different ways to sheet the mainsail when righting. One, to let it out, so the sail will dump any water as it comes up. Two, like you said, sheet in and let the wind help the sail up.
If the boat is on its side, don't worry about sheeting in the sail. With the bows pointed into the wind, if you get just a little of the mast out of the water, the sail will fill enough to lift out of the water and right the boat. Once the boat comes up, you want the sails luffing. If any sail is sheeted in, you risk having it power up and take off without you.
