This is exactly what happened actually in one of Valve’s court cases. It wasn’t that Steam went down, but rather the user was permabanned. When that ban happened he lost access to his game library. However, he had purchased those games so he argued successfully that he had a right to download what he purchased. Valve attempted to argue that they were a subscription service so that they would not have to provide anything to him. In the end since he won the case, he was allowed to download what he purchased. I’m sure that created a weird situation for those publishers and I’m not sure whether or not Steam had to remove the Steam DRM prior to allowing him to download.