My marina pulls a couple power boats a year out of the water and cuts them up. I have no idea where the fiberglass goes but it disappears. I'm guessing the owner is way past due and the marina has no way they'll get rid of them if they don't cut them up. If I ever see a sailboat come out I'll probably talk to them about getting the mast, boom and other easy to move parts as usually they hold a much better than scrap value. I've bought and parted out small sailboats that were junk in the past.
There are a number of boats at my marina that are probably only there as the cost of disposal is higher than the slip fee. I have a friend trying to contact a guy about his custom 40 ish foot sailboat that hasn't moved in about. I'm guessing it's a wreck but might be decent.