That's exactly it. If the device is not turned on, it will never receive the alert unless it checks in with Jamf Pro, which it remains a computer record and takes up a license. Which is not a big deal, you pay annually for licenses, so it doesn't really matter if you just leave it alone until the device shows up.
If you decide device is missing and you are writing it and removing it from your inventory. If you are doing that, then you can just delete it.
One other thing if you want to keep it around but delete it from Jamf Pro and get license back. Delete computer record in Jamf Pro. and just leave it in Apple School or Business Manager, whichever you use. Therefore, if you set it up to get a Pre-Stage Enrollment if the device ever turns on it will show up again in your Jamf Pro, and not use a Jamf Pro license until it does.