That can be repaired but the tailwires will have to be sturdy enough to carry the load .
I would index the two pieces together using several round tooth pics as joiners then epoxy the stab back on with 30 minute epoxy . Use eough epoxy to create a small fillet around the stab . Make sure the stab is positioned in alignment with the other half while the epoxy cures . After the epoxy has cured you will need to use functional tailwires on the tailgroup . Some kits only use light wire to create the tailwires . You will need to use something more substantial to support the stab. I usualy use 4-40 rod and clevises or the Dubro tailwire ends . you may also need to add some ni rod inside the stab at the tailwire mounting locations to add strength so the balsa wont crush or rip out .