Sacred Haven of Debauchery

But the problem of connection instability (and not its speed, why would it need fast internet?) could lead to not-so-pleasant consequences.

In theory, yes. But all these tricks with protection are relevant in the first 2-3 months, at the peak of demand for the game. After that, you can release patches that will remove all these contortions with the disc in the drive, mandatory online connection, and other things. Sometimes they do it that way. Also, I think the game won't freeze; it will pause until the next connection, and it won't pause instantly, but after a couple of minutes (in case the connection is restored?). In any case, that would be more user-friendly.