I guess they made a center board designed PY 26? Is this correct?
This spec calls it a fin keel: PACESHIP PY26 sailboat specifications and details on sailboatdata.com
We've all had bad days with our boats and thought: "How in the he!! am I going to fix that?"
Time, persistence and patience usually win out if you don't give up.
If the board does not provide much weight or ballast for the boat you should be able to sail even with the board locked in the "up" position. Hopefully there is some kind of fixed keel that has some weight in it, enough to sail with perhaps reefed sails.
Here is what I think I would do.
Get a bunch of Butyl tape or your favorite kind of underwater putty - I'd use Butyl tape - easy to apply and clean up.
Loosen the pivot bolt for the top half of the board. Make sure the other half can be lowered by its pennant.
Get the diver back or get a friend to snorkel under and grab the pieces as you lower them into the water.
The Butyl tape is for helping to stop any leaking that might happen when you remove the pivot bolt or lower the other half.
Retrieve both halves of the board. Weigh it - expect it to weight around 100# so I'd want to attach lines to hold it to the boat while it is in the water - to keep both pieces from falling to the bottom.
Find a welder or metal working shop. Have them make a new core out of metal (I'd say a decent grade of Aluminum - no rust), with an oversized hole for the pivot and lifting pennant. Hopefully wont cost much more than $100. Your new core should be smaller than the overall dimensions because you are going to laminate it with epoxy and cloth to bring it up to a more appropriate thickness. Sand it smooth or fair and paint it with bottom paint. Re-install.
You might even be able to scavenge a hunk of marine grade aluminum out of a dumpster somewhere.
I'd look at this more as a blessing in disguise than a total Debbie Downer as you ought to check out the pivot pin to check for wear and the lifting fittings on the board that may need replacing too. As others have said, you are lucky it happened at the dock. Could it even have been broken or about to break when you first bought the boat? Chances are it was about to fail anyway.
My boat also has a center board and as you say, when we run aground it usually just pushes the board up, without shearing it off. It is best to keep the board mostly raised though when at a dock or moored.
Take a deep breath.