Remove them and have them inspected/cleaned
Heed John's advice on doing this only if the boat is still in the water, on a cradle, or if there is absoutely NO wind when on Jackstands (poppets)...Albeit I have to (drop mast every year), I would remove them no matter what.Also, just because your Mainsail is an in-mast furler, water will still get in during the winter, possibly causing mold/mildew or freezing damage (Dacron resists but is not impervious to mold/mildew -- and needs air to do so). This is much the same as with the reasons for removing the furling headsail, albeit wind damage shouldn't be possible with your main.Further, removing the sail will reduce 'weight aloft' (better for the hull during lay-up) and de-stress all the bearings and lines of your in-mast furling system.That said, Consider opening up the sails when there is little wind, hose them off as much as possible, let them dry (maybe by going for a sail, hey why not, right?), then Remove them, and...assuming you have not already had them removed and inspected during your purchasing process, Have them inspected and repaired (if needed) by a good sail loft.The nice thing about sending them to a sail loft is they will also typically store them over the winter for you, reducing mold/mildew concerns if stored in boat, or finding a good place for them at home.Also, if not cleaned within the past 1-2 years, also have them cleaned.Regarding cleaning, do ask how they clean them though as some just soak them all rolled-up in a 'big vat' which doesn't really do much more than you could do/did with a hose.Hope this helps..