If you have been using iOS 8 and have noticed that some of your additional ringtones purchased through the iTunes store are missing, then you should update to the latest version of iOS. A short while ago Apple released the latest iOS update, brining its latest mobile OS version to 8.1.2, which includes several minor patches, but which most prominently includes a fix for a bug that causes ringtones to be deleted.
Even if you are not experiencing this specific issue, as with all patches, Apple includes security and stability updates, so be sure you back up your iOS device and then download and apply this update.
If your iPhone or iPad is relatively full, then you might need to use this later approach. Additionally, if your iPhone is below 50% charge then you will need to have it plugged in to update, so using your Mac might be a quick and easy approach for this. Using your Mac also has the benefit of allowing you to back up to your Mac, instead of only to iCloud.
Sadly, iOS 8.0.2 no longer lets me sync my devices by WiFi to iTunes 12.0.1, although wired syncs still seem to work. Apple really does seem to have problems with wireless.
Happily, iOS 8.1.2 (not 8.0.2 as I wrote) will sync but required a reset of Network Settings on each device, reconnecting to my local WiFi network on each device, and renaming each device names from the generic “iPhone” etc. to the names I had previously set. This is still a major annoyance for what should have been a simple upgrade.