You could easily ask the seller to pay a year of MFs to keep the contract active. All contracts have a date by which ownership needs to be transferred. If it misses that date, you're free to go--or you can use that to negotiate something (like a year of MFs, for the missed opportunity of booking a room early for your vacation, as this was the seller's error).
Other thoughts:
- in terms of the calendar year, this is probably the worst time to buy. Summer typically brings in a low of buyers. Not many great contracts out there to be had. If you back out, wait until Nov and Dec, some sellers will want to deal then as they won't want to pay MFs for 2025 in January. If you walk from this contract, either you look each morning and hope to get lucky or more likely wait a few months until the end of the year to find a good deal.
- Seeing what the Poly incentives are is a reasonable plan. But I wouldn't get your hopes too high. I think it's more likely that
DVC will have a huge sale on those cabins. Poly is going to be more popular than other recent DVC offerings, so I expect the Poly incentives to be mediocre at best.