Maintaining the same functionality advertised or realised at the time it was purchased.
WoW launched in an essentially unfinished state. Molten Core, the first 40-man raid, didn't have a loot table. I'm not sure it was even accessible on launch day. And when it did get a loot table, it had placeholder graphics for the tier 1 set.
This was fine: it would take months for players to be able to tackle end-game content, so the game didn't need to launch with it all ready to go. But a law requiring Blizzard to keep a launch-day WoW available wouldn't be especially satisfying.
Even if you changed it to be "its full functional state" or something similar, that gets weird. After Molten Core was BWL, which you couldn't reach on launch. And so on and so forth. WoW changes a ton over an expansion, and each expansion brings even bigger changes (do you play pre-Cata or post?). Do we require Blizzard to keep available each and every patch version? Hotfix version? How do players decide which they want to play? I really enjoyed the Argent Tournament, but I bet most preferred actually reaching ICC (which itself had a bunch of time locks before you could reach Arthas, himself).
[1]: Even beyond everything outlined, WoW gets weird when you consider Classic and now Forever.
An ever-evolving game with properties of a SaaS would likely not exist under this new law.
Blizzard already knew how to build self-contained products with self-contained expansions even before WoW was released. StarCraft was the original game and StarCraft Broodwar was the expansion. It will affect game release cycles and properties of what you get with the game, but that's seems like part of the point of the legislation.
For example, massive expansion of free to play games with cosmetic microtransactions.
When the game ends... what is it that you've bought? The cosmetics, you never bought the game. If they give you an offline "shooting range" mode where you can wander the maps in the cosmetics you bought, have they satisfied the requirements? Again, you never bought the game you bought the cosmetics.
A step farther, loot drops in loot boxes that take time to unlock, on the order of days, weeks or months. You buy something to accelerate the unlock process down to hours. What have you bought? Just a faster unlock of something you'd have received anyway. So what are you owed when the game goes end of life? You didn't buy the game, you didn't buy the contents of the lootbox.
This is actually true of a large market segment.
Consider, there are existing laws against libel which were written before video screens existed. Did those laws encounter insurmountable, analogous circumvention issues when the printed word was no longer "printed" with ink?
Problem is with “purchase” imho.