Apple Music offline downloads validity period without internet?

Is there a time limit to how long Apple Music downloads last while offline?

My daughter will be at sleep away camp next summer, and since they're not allowed to have phones, and Apple has stopped making iPods, I'm looking at digital audio players (many of which seem to be simple, locked-down Android devices). Several of the ones that are marketed towards kids like her say that they do not support Apple Music because of complications with offline DRM.

This got me wondering, if I do decide to go the Apple Music route (I'm already paying for a family subscription and would rather not buy her Spotify Premium on top of it, plus I prefer to stay within the Apple ecosystem when possible), and I get her a device that has Apple Music on it, what will happen when she downloads songs and then is offline for a month (or more)? Will the songs stop playing (or, worse, erase themselves) if the device can't "phone home" and verify that her subscription is still valid? How long will it be before that happens?

I do realize that this question has been asked before; unfortunately, it's never been answered clearly, it seems. I'm hoping that someone from Apple Support (or someone who can point to an official resource to verify their answer) can tell me. Thanks!