Hey Dan - I would definitely trust that car to do ok in an accident, save some assurance on that thickness of metal he used, as I wrote.
Frankly, while I don't know what the level of roadworthiness inspection is in Canada, I can say that in California it is non-existent. Only emissions is checked here, quite thoroughly in fact, but absolutely nothing else (brakes anyone?). There must be quite a few rust buckets driving around here that would not hold up in an accident for sure and the authorities don't seem to care. THis is quite different in the other countries I've lived, Netherlands, Switzerland and France - any rust is frowned upon and structural rust is pretty much a guaranteed fail.
The Lancia I am working on at the moment was not quite as bad as this Mercedes, but close to it, and I am very confident that the repairs I did will be as effective, safety wise, as what a professional shop would have done, using only slightly more professional methods than did the guy in this video. Ditto with the Volkswagen I gave a new lease on life earlier this year (although that rust was less structural and more cosmetic).