There are too many 2042 resorts that would expire all at once. I bet there will be an extension offered on some, and no extension offered on others.
If we leave Vero and Hilton Head out of the discussion, there are only 3 resorts: BoardWalk, Beach Club and Wilderness Lodge. Combined they represent about 700 DVC villas. Not a huge number, and all very popular destinations.
Assuming Disney doesn't embark on any major plans involving demolition / reconstruction, they will start by offering new 50-year contracts to existing owners. Barring any legal hurdles, they could begin that process 12-18 months before the 2042 end date. IMO, they'd sell several million points to owners willing to extend with very little sales & marketing expenses involved.
Then they could open sales to the general public, also well before January 2042 when the new owners would be able to start using their points. DVC has pre-sold resorts in the past, giving the buyer developer points for use at a different location until their owned site is available for use.
They could also choose one or more of the resorts for an elaborate re-build. Beach Club would seem to be a prime candidate. Use the existing land and perhaps extend out into the parking lot for something larger than the current 200 villas. With BCV out of the picture, DVC is only re-selling the 500 or so rooms at BWV and VWL/BRV.
OKW has both 2042 and 2057 contracts. I would bet Disney will offer a 15 year extension for the 2042 group starting no later than 2027.
To the best of my knowledge, the 15 year extension is still available for OKW. It was initially offered at $15 per point for a limited time, with the price later increasing to $25 per point.