Lets pretend this law was in place before WoW released. What degree of functionality would it have to retain to be compliant with this?
Not totally clear at this point.
The initiative asks for nothing more than an end-of-life plan for a game for AFTER the dev/publisher has taken it offline.
In what form exactly is then up for the EU Commission to determine.
The initiative itself is vague on purpose here:
The initiative does not seek to acquire ownership of said videogames, associated intellectual rights or monetization rights, neither does it expect the publisher to provide resources for the said videogame once they discontinue it while leaving it in a reasonably functional (playable) state.
"Reasonably functional"
Now, that sounds vague, but it answers a lot, actually.
Is it reasonable to expect publishers to keep hosting all online functionality on their servers AFTER they take a game offline? No.
Is it reasonable to expect players' data to still be available after the servers by the publisher are gone? No.
So, in the end, the most likely scenarios will be providing players with means to host themselves (even if that means local only) or to make the game playable offline and merely mock server functionality.
At least that's how I see it and how Ross himself explained in some videos, too.
That's not optimal, but in the case of an "officially" dead game, it is reasonable - and obviously much better than the current "nothing at all, ever again".
In the case of WoW, my personal minimal expectation here would be a kind of single player mode without any of the multiplayer features.
Hopeful expectation would be a means to host actual servers myself. Database schemas, API documentation, etc, optimally server executables themselves (though that might not be feasable in all cases).