what about physical damage. or emp or something. I feel like that will be a problem well before 200 years.

Mold is actually the biggest concern with the most popular archival format LTO. EMPs aren’t that much of a concern. Bit flips and bit rot are your main concerns traditionally when using flash for archival storage. It’s recommended if you go the flash route to keep your array hot (ie powered on) and use a file system with data scrubbing capabilities such as ZFS.