HH,
Wow. That doesn't sound good at all. From your description then, the mast did not fall. Have you secured it with halyards? The best thing would be to have it pulled if you don't think it can be secured safely.
Having never experienced that issue myself I can only offer what I have read. Also, I have attached a .pdf file from both the original brochure and my owners manual that shows the construction details. Somewhere back in the archives may be some discussion about repairing the chain plate. The cause as I recall was due to water running down the tie rod (sealant failure on the deck) and rusting that iron angle. At some point it pulled the 3/4" nut right through the iron. It is not stainless (the rod and nut are, not the anchor). The repair approach was to open the hull from the outside to perform the repair as that portion of the inner liner that it pulls up on should be left intact. There just doesn't seem to be anywhere to slide a new chainplate anchor in from the inside, if that is your issue. That kind of repair would be beyond my pay grade. Maybe insurance could cover it. I don't think it is a particularly difficult task if it is just the iron that needs to be replaced. That job needs some real good expertise in closing up a hole in the hull. The hull would probably have to be painted afterwards. If your failure is due to pulling out the fiberglass liner (longitudinal step) That will require even more engineering to fix.
Maybe you can post some pictures as there are many of us interested in this failure.
Allan