An Xbox can play all games that have already been downloaded and all physical disks indefinitely, regardless of whether you have internet or whether Microsoft's servers are up.
While correct, that was not the point made in my comment. For downloaded games, once the service has gone offline, you are at the mercy of the lifespan of the hard drive.
If I had a physical disc, I could just buy another when it goes bad.
Not sure about Xbox because I haven't owned it in a while but PS4 lets you copy your system drive to a new drive pretty easily. The function is even built into the OS. I switched out the hard drive to an SSD using this technique.
