For me I think Physical BTC Wallets will last very long and it depends on the BTC wallet provider hardware on how they maintain those hardware.
But we can assure on those legit BTC wallets that they have strong foundation of software and hardware before they go on BTC business.
This is the paradigm of long term information storage. The solution isn't in a permanent material or permanent device, it's the most inefficient way to address this. To hell with substance permanancy. This is money, keep an eye on it. Beause the information is the key, I think it's better to hide something like this in plain sight. Religions figured this out centuries ago; you want to hide something really important, encode into a public document and give the key to the people you want to understand
I just gave a way a secret, if you caught it
Make a framed picture of your key, hidden in a poem. Make a charm bracelet out of your key. You can even print it out. The winning strategy is to make redundant copies. It's the halfway point between concelaing information for its sensitivity, vs exposing information, even if encoded, for its longevity.