The Web was supposed to be robust (e.g. to nuclear attacks), but in reality it's very fragile and temporary. See how many dead links, dead domains etc.
another site that has survived its owners passing is this still popular #cyclists resource.
Sheldon did however have a very supportive network of friends and family, was open on his blog about his significant health problems in the 2000s and also had links to a still extant bicycle shop so there was a good body of resources available to keep the web presence running