how many key/critial kicks will Grupe miss before it costs us

You can't possibly be serious. The man hit 5 of 6 kicks. He should've never been kicking that much to begin with. And on top of that...do you really think the offense would've gotten an onside kick...and then somehow miraculously done something they had not done all game...and scored a TD?
Anything short of 7 out of 6 won't be enough.