I get asked this question all the time from people who split their databases and want to set them up for multi-user access: "if you give users read/write access to the folder on the server that holds the database, can't they just delete the file (either accidentally or intentionally?)

Yep. That's a risk you take with Access. People need read/write privileges to the back-end folder. If they know what they're doing, they can open up your tables directly, or even delete the database file altogether. There's not much you can do about it. That's why you need good nightly backups, saved in a secure folder. You can also encrypt the data in the tables so if they steal the file, all they'll see is gibberish.But you really can't stop them from deleting the file. If you need that kind of security, then you'll have to upgrade the back-end to SQL Server.