At Walmart there is spectracide tree/branch spray that seals the wound......it might to too large of a chewing, but I would shake the can well and get up in & around all parts of the chewed area...........and then put fencing around it and stake it. It might save it.......I do that to the fruit trees when something cuts it. That keeps the juice from coming out in the spring when it comes up from the roots....don't use cement that will hurt the tree. It just happened this Nov, so the sap is probably down already, so you can safely treat it. Keep the can inside your coat to keep it warm and shake it to use it..........keep the can indoors to prevent it from freezing. Sometimes I have to clean it with a pin to open the spray opening. Good luck with your weeping cherry.