Yet… Ubisoft did go and “remove” the keys for the crew when they shut that one down. No one but them can really say if they actually deleted them or not. though I have my doubts with how that company has acted in recent years.

There are reasons for why that is possible, for better or worse.

To reverse malicious actions that may have been taken by other people that got access to the account for any reason for example.

There may even be legal reasons for why that is the case. Licensing law can be quite complicated.

And then there is the fact that if it’s hidden it’s effectively gone anyways and that may actually be what people actually care about. Not whether or not they technically still have that game or not. People wanting a clean library is a thing and it ties into the concept that is the right to be forgotten.

I can only speak for Deus ex: mankind divided since I have played that myself.

It is technically a sequel in the sense that there are other Deus ex games that came before it with the original Deus ex, invisible war and human revolution. That said every single one of those games has it’s own self contained story with only some overlap between them. Mankind divided features the same main character to play from the previous game but everything else is different. From the location to the characters barring one which isn’t an issue for reasons… And is also otherwise completely isolated from the first two games maybe with one Hommage that you might miss If you don’t know the first game but then it’s just a great character instead of the thing it’s supposed to be.

Long story short, IMHO you can just pick that one up and play it without worrying about missing a ton.