I don't believe you can repair this maple. What I have done in the past is cut everything off immediately below the wound. I have a Bloodgood I did this to and it regrew and looks nice now. You may try this. It will require some pruning over the years. Good luck.

That IS pretty significant damage, but I've seen JM's survive with worse :-) The bigger question is, should it survive, what is it going to look like? IMO, this tree will never regain a very appealing aspect and in such a prominent and conspicuous position in your garden, I'd seriously think about replacing it. I might not toss it out altogther but just relocate to less visible place and see how it goes.

I'd not recommend cutting it off below the wound. This is essentially the the equivalent of topping the tree. It removes the apical meristem and so the tree will never get significantly taller (not necessarily an issue with such a pendulous selection), can stimulate a lot of weird growth and exposes the tree to even greater disease vulnerability. I've seen this attempted on a variety of JM's and the result is not very pleasing.

gardengal--that is one of my concerns as well--it might never look good. And yes, we did select the location for a "show" piece. I may take this approach, perhaps putting it into a container for now, see how it does, and then eventually put it back in the ground if it does well.

Or is the only decent option put it in the ground somewhere else?

now that is real sad ,I think you should just come on out to Ca.and be done with all that snow!

But I like the snow . . . just not snapping my j.m.'s My mother-in-law did much worse. She had a 15 y.o. tree (similar habit) break all three main limbs.

Anyway, this is leafing out just fine now. One of the small branches just above the split is headed in the right direction. This may always be weak, but it will probably make it fine and ultimately be good looking. we shall see.