I just need to make sure they've removed the device from their iCloud right?
the more proactive and knowledgable apple support people recommend this:
1 make iCloud backup either to iCloud or yr mac just before going to the apple store
2 talk with the apple person on site at the store and let him/her know before doing this: sign out of Find My
3 talk with the apple person on site at the store and let him/her know before doing this: sign out of iCloud
the above will cause you to redownload any apple Music you want on yr device. but won't cause you to lose any data.