As long as the janitors aren't using electric floor buffers, like NASA used to do, the tapes will last forever. However NASA ended up losing the data (from 1960s space missions) on the bottom 2 rows of tapes. It took a couple decades though.

Example of those mag tapes: https://www.computerhistory.org/revolution/memory-storage/8/...

How they were stored: https://www.hewlettpackardhistory.com/item/an-attractive-sol...

The newer stuff is a heck of a lot better than the olden stuff.