The language is already there.
"This is an agreement to rent points that represent accommodations only ... Should accommodations not be available on date of arrival due to an action or omission by the Owner, including but not limited to negligence on the part of the Owner and after communication with the Intermediary, suitable comparable accommodations for the same dates cannot be secured by the Owner, the Renter will be due a refund limited to the amount paid".
Contract states numerous times that it's non refundable, with one clause stating an exception due to an action or omission by the owner, which isn't the case here. The contract isn't for a confirmed reservation, it's to rent points that represent accommodation. But again, it's a contract with three different parties, one of which is a Canadian, and the other two parties can be from different states in the US, or from another country. The chance of winning, and collecting if you win, is close to zero.
Now that I think about it, I change my mind on the chance of success in chargeback. Originally I thought it was much lower. But then it's really up to the renter to convince the issuing bank. The investigator at the issuing bank will look at the situation - renter paid for a reservation, DVC canceled it due to closure, but the "broker" won't give a refund. The average investigator at the issuing bank isn't going to understand all this DVC stuff and differentiate broker vs. Disney, and likely approve the chargeback. Then it's up to David's to present the case to his merchant bank, explain that the renter paid for points instead of an actual reservation, and convince the issuing bank to charge the customer. Again, common sense would dictate that the renter wins. Good luck with that.
Yeah... the outlook looks pretty grim for the intermediary I think. Just look at stub hub. If they have confidence in winning in a chargeback, they wouldn't offer 120% credit for future purchase, which avoids the chargeback. They won't be willing to lose 20% if they have confidence in winning the chargeback argument. This was from a company that was acquired for $4.5 billion in late 2019. You'd think they have the resources to hire lawyers and explore every possible angle. This is the solution they come up with - basically paying a 20% premium to any willing takers to avoid the chargeback.