It's not just about death, it's also about brain damage. A broken bone is NBD compared to a TBI with often permanent damage.
You can lock helmets with bikes if you want. I used to lock my helmet with my u-lock on my bike, so if they cut off the helmet, then it isn't a very useful helmet. I now bring it with me in my bag mostly for hygenic reasons although.
Personally I would avoid locking a helmet up like that.
Expanded foam helmets are fragile by design. They are design to be disposable with even small knocks. So even accidentally banging them against your frame, dlock or solid post is a bad idea even if you can’t visibly see any damage.
You’re recommended to replace them at regular intervals also due to sweat damage.
That isn't much of a solution in practice. No helmet manufacturer puts best after dates, other than in fine print nobody reads and practically nobody replaces helmets unless they see visible damage.
Then again 3cm of expanded polystyrene foam vs a metal box with a engine in it... probably like a surfer forgetting to replace their “anti-shark bite” medallion anyway.
You can lock helmets with bikes if you want. I used to lock my helmet with my u-lock on my bike, so if they cut off the helmet, then it isn't a very useful helmet. I now bring it with me in my bag mostly for hygenic reasons although.