Stainless steel is not some magic adamantium that is completely unbreakable. You can choose thinner steel for the part that is designed to crumple, and it will

Stainless steel is not some magic adamantium that is completely unbreakable. You can choose thinner steel for the part that is designed to crumple, and it will crumple or fold as intended, just like any other material. I would guess that the bonnet will move backwards and slide over the windshield, and the other part of the front (up to the front wheel wells) will be designed to crumple.