Members took out an insurance policy last October under which they each stood to receive $1m (pounds 625,000) in the event of alien abduction, alien impregnation or death by alien attack.
It was underwritten by British agent Goodfellow Rebecca Ingrams Pearson (Grip) who said yesterday that the policy could cost British insurers millions if United States inquest juries proved to be as perverse in this case as in others.
Simon Burgess, managing director of Grip, said that if a coroner's court delivered an open verdict, it would pave the way for the families of the 39 dead cult members to pursue claims through the courts. But if an inquest confirmed that they died as a result of suicide, the verdict would invalidate any claims.
"My belief is that aliens were not involved in these people's deaths. However, we have to keep an open mind," Mr Burgess said.
Goodfellow Rebecca Ingrams Pearson specialises in, among other things, insurance policies against alien abduction of humans and virgins becoming pregnant through immaculate conception.
The annual premium for the group, known as Heaven's Gate, but which carried the alternative name of The Higher Source in the insurance policy, was pounds 1,000 a year.
The cult, which ran an Internet web page company known as the Higher Source, would have known of the existence of Grip as its services are detailed on the Internet.
Grip has built up a reputation for broking unusual insurance policies. It has 4,000 clients worldwide insured against alien abduction, while several hundred virgins have taken out policies against immaculate conception.
The annual charge for such policies is pounds 100, but as Mr Burgess emphasised: "There has never been a genuine claim for alien abduction."