Tickets can be reassigned in MDE if your guest decides to back out. If you manage the guest's profile you can do that yourself; if your guest has their own MDE they would need to be willing to transfer the ticket back to you. You then have the credit to use towards your next trip.
By my rough calculations, your math doesn't quite work out. You'd pay ~$115 extra to book a package that you won't use the accommodations for a "free" cancellation period, but the 5% cancellation fee charged by a 3rd party site would be less than that (~$80-$90 depending on dates). You are renting DVC which usually cannot be cancelled, so you have funds sunk into this trip regardless. I'd wait until closer to the date so there is less chance of needing to cancel, and watch for a good ticket offer from the 3rd party.