The chassis has very little to do with how well a camera survives a drop or a simple impact or glancing blow; the CRITICAL part is the outer shell. Metal dents. Polycarbonate does not. Old, heavy, metal top-plate and metal baseplate cameras often suffered when they were dropped or impacted..."cheaper" cameras with polycarbonate top decks and bottom plates flex a bit, and you dust them off and say, "Whew...it's okay!" This is what I learned working at a camera store, from the experiences of hundreds of our customers. BIG, heavy "solid" rigs often fared the worst. Cheaper, lighter, "polycarbonate" amateur stuff usually fared okay.
It's a lot like the way we transitioned from solid, steel car bumpers to soft, polycarbonate, foam-filled bumpers...bumpers that actually PROTECT, rather than transmit every iota of force that they receive in impacts. The chassis is protected hugely by the outer shell. If a drop or impact is strong enough to rip out the mount's mounting screws, then you might be hosed, but short of that, the chassis's material is more about marketing and hype and price justification than ANYTHING. Cameras have been made of wood; plastic; aluminum; brass; steel; magnesium alloys of multiple varieties; titanium; polycarbonate; and many,many mixes of all of the aforementioned materials. The chassis is of minor importance in drop damage; other factors really are the critical ones.
Which will fare better: A magnesium-alloy chassis "professional" camera dropped 25 feet and onto asphalt, with a 70-200 f/2.8 annnnnnnd a tripod mounted to said lens? Or...a polycarbonate Canon Rebel that drops 22 inches with a six-ounce, all-polycarbonate, 18-55mm kit zoom mounted onto a vinyl dining room floor?
My money is on the cheapie rig faring better. Farrrrrrr better, in like 99% of instances.