If you and the dealer have 21 and you don't insure your hand do you lose or push?

Insurance is like a side bet that the dealer has 21, it is only offered when the dealer has an Ace showing. If you decline the insurance bet and the dealer has 21 then it is a push, if you take the insurance then you push the hand and win the insurance. When a player has 21 it is never a loss. A 21 is a guarantee that you will not lose, the worst case scenario is that you will push.