Nobody would buy a game that says it is only guaranteed playable for one day.

What they need to clearly state are expectations on planned lifetime of authentication servers, any specific technology that is required, and so on. Like people know multiplayer requires servers, but something that says they will have those servers for X number of years would help set expectations and encourage companies to plan long term support for games that might not be massive hits.

For single player games this would discourage terrible DRM that keeps games from being played just because authentication was retired.

I disagree.

The devs that don’t do that would stand out a ton.
Plenty of meaning to me.

Non-permanent games would be easier to identify, so plenty of devs would add an end of life plan just to stand out.