how long will vintage cards physically last?

[drcy]

Old documents used to be on parchment and vellum (animal skins). Don't know how they have lasted.

Interestingly, before canvas, paintings were usually on wood. The Mona Lisa is on wood.

Dust and dirt and exposure is a big cause of damage, so entombing them in a holder is likely decent protection for cards for long term. Though probably sealing them from air between acid free sheets is probably the best.

As mentioned really old paper can last better than a lot of modern paper, because rag paper doesn't deteriorate while wood pulp in modern paper does. However, many modern artworks, including prints, are on rag paper so should last well.