What are a Dog Breeder's Responsibilities?

Thought I'd put an innocent question out there to the blogosphere. I would like to know the following:

If you are sold a purebred dog, many of which are prone to some genetic, breed-specific "deficiencies" and are guaranteed against any of these deficiencies and your dog is 6 months old with, the absolute worst case of this deficiency a vet has ever seen in a dog that age in his entire career, what are your options?

I cannot imagine this scenario being a dog-lover and past dog owner myself. I cannot imagine falling in love with a new member of the family for 6 months and then being told by your vet that your only options are a) extremely costly, extremely invasive surgery you cannot afford or b) putting the dog down.

Right now I am researching this...getting some feedback. Would love your input.