I would go off points. I know it's the boring decision, but then you are guaranteed to still keep the game going if something malfunctions. For example, if the game was Metallica and the goal was Graver Digger Multiball and the grave marker at the end stops registering hits, you have to take that game out of the tournament and everybody who already played will have to play a different game. This way, if the grave stops registering, it's okay because you can grind out points a different way. Plus a points goal allows you to award/penalize progress towards a goal and will minimize ties.
For example... let's say the goal is 10 million.
0 - 1,999,999 +5 penalty strokes
2m - 3,999,999 +4 penalty strokes
4m - 5,999,999 +3 penalty strokes
6m - 7,999,999 +2 penalty strokes
8m - 9,999,999 +1 penalty stroke
Those penalty strokes would be tacked on to the 3 balls they played in their game when they fell short of the goal. So the best you could do on a hole is 1, the worst being 8. It will lead to a lot more variance in scores.
It's also super easy for scorekeeping purposes if you print those penalty stroke ranges and tape it to the backbox.