Several posts on the Xbox forums are revealing that people with full paid games are finding they stop working when the game pass is cancelled etc. Xbox support suggested spending money and buy the game again when its already paid for. Nobody wants to pay double for the same game.
Clearly the console peasants are screaming loudly over the lack of adequate tracking of purchases to prevent this fiasco from happening in the first place.
Not many new game discs for the Xbox Series X but existing Xbox games will work. The studio suggests sticking with physical disks and avoid the Xbox store outside of game updates. This approach avoids the fisco of buying games that disappear from the account.