I'm just going to buy it physically.
If you're playing a game that relies on downloading patches (which is like 99% of games at this point), you're still at Nintendo's mercy. Buying physical at this point is kind of stupid. In addition to wasting space, the thing that's in the box is rarely a playable game any more without an internet connection and it's almost never the complete game. You buy something on Steam, it'll work on any desktop/laptop that the game supports (and Windows compatibility modes work pretty well for even those older, "unsupported" games) until the heat death of the universe. Once again, there are people who don't give a shit about that and that's fine, I guess. But there are plenty of reasons not to buy shit on a Nintendo platform unless you have to.
Also, wouldn't the same rules apply to Steam? Don't games get delisted?
Almost never and the rare times they do, it's the publisher that does so, not Valve (usually because of a licensing issue). Steam is by no means perfect (particularly on the developer/publisher side... it has a notoriously haphazard approval process and terrible game discovery) but they've ironed out 99.9% of the technical and interface issues and Valve is by far the most consumer-friendly of all of the digital platforms.
And not for nothing, Nintendo has not disabled your ability to re-download purchased games:
Even after March 27, 2023, and for the foreseeable future, it will still be possible to redownload games and DLC, receive software updates and enjoy online play on Wii U and the Nintendo 3DS family of systems.
Give them time. Wii downloads weren't available at all for months last year because Nintendo decided they needed to perform "maintenance". Nintendo is notoriously cheap. The second they think they can take down those servers without too much pushback, they will.