In my opinion you should get the old blade plus the new blade at least. Even if it is a user CR knives carry considerable return value, and the BG blades have gone faster and for more IMO. The fact that they broke your blade without telling you the risks means (to me) that they should do what they can to make you satisfied. Honestly if it was me representing the company and my hands were tied, but it was our responsibility for damaging another's item, I would offer a complimentary FB or some such as an apology. "This is your only option" is not working with the customer- it is giving an ultimatum. Take it or suffer with our mistake does not make me satisfied.
Personally I have never understood the "it's BG42, we can't replace it" line from ANY company. On anything with a lifetime warranty it is irresponsible for the factory to run out of materials and try and say they cannot get more. BG isn't common, but it is available, so (to me), the manufacturer should be able to replace the part- especially with something as basic as a Seb. The patterns have not changed so drastically in this amount of time. If you offer the warranty, keep the dies, as well as a selection of the steel used for these cases, as I am sure any company expects this kind of thing to happen. The comment about "what, do you want him to make you a new blade" strikes me as odd as CRK is the manufacturer, so yes, I would expect the manufacturer to be able to reproduce a product they produced in the first place. The only time I would lighten up in my opinion is concerning natural materials, but that is only not guaranteeing matching of figure/characteristics of the wood.
I have a single Seb, like it enough, and do not consider it the end of knifemaking. It does concern me that the manufacturer with the tightest tolerances isn't able to make a blade to replace one after they damaged it.
Your opinions may vary but with so many awards for manufacturing this is an unacceptable response to me.