The resorts are insured. If there is a catastrophe and the resort is obliterated, it will be evalutated and if it is deemed that it "isn't worth repairing" the insurance will be distributed amongst the owners and they will no longer be
DVC members. If the resort needs major repair, but is deemed repairable, any expenses not covered by insurance and other available funds can lead to a one time special assessment, and in fact, owners at Vero Beach were told to expect such an assessment after the hurricane damage a year or so ago. However, available funds did cover the repairs and the assessment was not needed.
DVC also has the ability to restrict usage of your points while your resort is under extended repair, where you could not use your points at all, as your closed resort would have no "trade value."
BTW, these things don't neccessarily apply to a resort as a whole, they could also apply if the particular building where you are deeded is destroyed...so while unlikely, in theory if your building is destroyed by fire you could be denied use of your points, even if the rest of your resort is undamaged. I doubt DVC would ever enforce that, but it is in the rules "just in case."