I guess they'd be unsuable but would a new set need to be made then? Would the past set simply vanish or turn to stone?
While Super Saiyan 3 Gotenks fought Super Buu, Piccolo stated that if a single ball was destroyed the entire set became useless.
It makes sense to think that the set just stays there looking like pretty trinkets. The balls turn to stone because (I assume) their magic was used up, but breaking a ball doesn't affect the magic of other balls.
This only applies to the Namekian copy balls. For the planet sized super dragon balls, we don't really have enough information