How many pain killers ie oxycodone hydrocodone would cause an overdose effect?

Totally depends on the dosage involved, the tolerance and size of the person involved. Each person is different - someone not tolerant to opiates would succumb to respiratory arrest fairly quickly if they took too much, while someone like me who has used it for many years actually only gets increased side effects.

One possible outcome would be that the person could OD and not die at all, just wind up with brain damage. There are things worse than death.