I see what you're getting at but this would be difficult for a publisher to stick with in the event the game does horribly. Requiring them to keep their word to the date advertised would end up with them only guaranteeing a week, or send ramifications through all industries requiring truth in advertising.
A middle ground would be simply to legislate that when games require online connectivity for any reason, the appropriate software is released to allow a locally run server to enable online function at the time the company decides to decommission their servers. Then require them to hold these files in an accessible manner for at least as long as the servers had been active for.
That would be difficult in the event the company goes out of business, but I'm sure this would be a difficult thing to explain to most politicians so maybe not so simple after all.