The expiring resorts are HHI, Vero Beach, Beach Club, Boardwalk Villas, and Boulder Ridge. Old Key West is NOT expiring, it has already been extended to 2057, but a large number of people will be giving up their rights to use it, after 2042. Only those who paid for the extension will still have it.
Disney will most likely sell off HHI and Vero Beach. The are not that popular, they are not that profitable, they are worth less per point than other resorts, and there is no real reason to keep them, since their original purpose was to help Disney broaden and expand DVC, but they failed in that, for the most part. ALSO, Disney has undergone a change in philosophy, from making DVC into an amazing timeshare that would serve all 'Vacation Club' owners, into a much more focussed, money making pipeline funneling people directly into Disney World. Perhaps the main reason Disney is likely to sell them off, is because they drag down the value of DVC points. This makes it harder for Disney to sell the more expensive points at other resorts. So HHI and VB probably don't need to be a part of the future of post 2042 DVC.
BCV, BWV and Boulder Ridge have a total of about 1000 units between them. A bit more units than are in the resorts of OKW and AK (both of which have a little over 700 units), but significantly less than SSR, with 1300 units. Disney will probably take all three of those resorts and immediately start renting the units out, while reselling them as quickly as possible, as new DVC units. They might remodel some, but DVC Membership Dues should have maintained them in excellent shape, and they pretty much will be ready to turn around and be rented or sold almost immediately. Why would Disney tear them down and go to the additional expense of building new units when the currently existing ones will be doing just fine? I know that we, as American's expect that buildings will be new, but that is just because of the 'brief' age of our country. I was recently in Europe where many fine hotels have been in use for over 200 years, as hotels, and are still doing just fine. I don't see why Disney would need to tear down buildings that are only 50 or 60 years old.
It is not clear how much of OKW is owned by people who have extended, and what percentage is going to expire, but there will probably be a not insignificant portion of it that will be looking for new owners after 2042. On the other hand, Disney has been exercising ROFR on Old Key West at the rate of about 80 contracts per year. Clearly, if they keep this up for 10 years, then through their ROFR they will end up converting most of the 'expiring contracts' into 'non-expiring contracts,' since most of them will have been extended by 2042. 80 per year for 10 years is 800 units, which is more than the total number of units at OKW. Still, however many unextended units remain, those units will be added to the sales inventory, BUT, they will be short term sales of 15 years or so. I DO believe that Disney will try to sell them, just in order to avoid paying the Maintenance Fees, but they won't be able to sell those points for full price. And if they think current 'Resales' with discounted prices is adversely affecting their more expensive Direct sales, then I see OKW at 15 years as being an even bigger problem. There are certainly many people, who would jump on an OKW contract giving them 15 years for $70 per point, rather than a more expensive 50 year contract somewhere else at $200 per point (equivalent, adjusted for inflation). So, unless they 'convert' most of the expiring contracts into extended contracts by then, it could be a problem for them. My guess is that they are doing just fine, by picking up OKW with ROFR at the rate they are, and so this probably won't be a problem.
So that still leaves the question of what they will do with BCV, Boardwalk and Boulder Ridge in 2042. I think it is likely that Beach Club will just be converted into a 'Villa Hotel.' It is a very desirable location and they will almost certainly NEED the hotel rooms by then. And they will put the Boardwalk and Boulder Ridge units on the DVC market, while also using many of them as hotel rooms in the intermediate timeframe. If they are not trying to sell BCV as DVC, then they other resorts will give them a total of around 700 'new DVC units' to sell. This is quite manageable. And with proper planning and preparation, and by not building any more DVC units in the last 4 years before 2042, I really don't see Disney having any problems. DVC will be 'refreshed' and will continue to go on as it has before.