Under US law, no party to a contract has a responsibility to mitigate damages to another party.
You've also greatly simplified the relationship of the parties, which is how a court would determine who takes the loss.
The owner has a separate agreement with David's which laid out the number of points, when they expire, and how much David's is to pay and when. The payment terms are 70% of the fee at booking, and 30% on check-in day, regardless of whether the renter checks in. David's has, apparently, breached that agreement by withholding the 30% payment for rentals which occurred when the resort was closed, and is asking owners to re-book and wait on that payment until the new reservation check in date or to refund the deposit payment. While the resort closure we now face was not contemplated by the contract, the broker, who drafted the contract, knew that such a situation could and has occurred in the past. If the situation was known, and the broker chose not to include it in the agreement, he cannot then unilaterally re-write the agreement to benefit himself. David's owes the final payment on the original check-in date. Period. Full Stop. Anything else the owner and David's agrees to do is open to negotiation, not what David's says will happen.
The renter has an agreement for a room reservation with a no-refunds and no-changes clause. Strictly under the contract terms, the renter is losing everything. Under consumer protection laws which may be in effect based upon where the parties are located, which supersede the contract terms, the renter is due a full refund. David's has offered a voucher program instead of refunds. Whether that is legal under Canadian law is a question that hasn't been addressed.