There's a shot at a repair, but as you've said, it wouldn't be pretty. The threaded collar that the allen screw goes into would have to be re-epoxied. I'm assuming it was epoxied and not threaded to the plinth . So the best approach might be make the best cosmetic/structural repair possible, then re-drill the hole for the collar. Another approach from a cosmetic point might be to fab up a small metal plate with the collar hole centered to cover the damaged area. In a perfect world, perhaps even a new threaded collar that affixes to the metal plate. This would cover the damaged area and structurally hold the collar without the need for epoxy. Lots of options, but the table should be disassembled before starting any surgery. But when all is said and done, the best way to actually maintain the value of the table is to replace the plinth.