All good questions, if you were buying insurance and I ask similar questions when i recently changed insurance companies on my house. The big differecne is that PrivilegeFlyer has stated for over 12 years that it's not in the business of insuring your miles. It's in the business of helping members get more out of their frequent flyer programs.
As for your other questions, you might re-read the information available on the Web site - it appears that neither Ansett, National or Canadair were ever included in their AwardGuard benefit, so it seems a bit unusual to inquire of that issue. In 12 years you'd certainly expect that anyone having any problem - even the smallest would have complained and there would be a record with the local BBB or elsewhere. There doesn't seem to be any record of any complaint in 12 years - amazing record of member satisfaction. And while there have been just a small number of frequent flyer programs that might have been covered in their protection, it does seem they covered expiring miles for American and United for ten years (all before FlyerTalk and the popularity of the Internet. Since those were huge programs and every member had expiring miles, there must have been thousands of people who protected their expiring miles while using their other program benefits. Seems that all those members must have been happy with their benefit claims since again there are no record of a single complaint. As for exposure? As I think they (PrivilegeFlyer) are the insured with what is known as Contractual Liability Insurance, and their rulles seem to indicate that their first knowledge of any liability would only come at the time a program goes down - they really would not have a way fo knowing exposure other than to carefully choose who they purchase insurance from. But that's their option and choice.
In the meanwhile, you sure seeme to get a lot of stuff from them that ultimately seems to help you earn more miles and points. I hear that the roots of PrivilegeFlyer are from their Frequent Flyer Club that they started back in 1987. For most people on FlyerTalk - it's hard to believe that these guys were "into" helping people with their miles that long ago.