That's pretty much it BB. The fact the keyway was damaged means the balancer had been moving around. This will either micro weld the crank to the inside of the balancer or it will machine down the snout of the crank. This means any new balancer that goes on or the old one, will not have enough or any interference against the crank snout. The amount of movement there when you are revving past 7k would scare you. The purpose of the balancer/dampener is to remove harmonic vibrations from the crankshaft. If it is able to move due to the bearing retainer or loctite material not being able to sustain high bonding strength for more than a short time, it will surely come loose again or destroy the oil pump.
I know people who have welded balancers on to cranks and not had problems. I know people who have repaired keyways and not had problems, I also see the ones that were apparently repaired correcty and have come unstuck. If it were my car and I had to choose, I'd choose to replace it.
If the repair is done by welding the snout of the crank, you also risk the end of the crank snapping off. I know people had done this without any problems but once again, I have seen the other side of the coin too. Why risk it. Cranks are not expensive and fairly easy to come by