Google will automatically delete your Android backups if your device remains inactive for two months consecutively.
Google will automatically schedule to delete backups of your Android device if the device is inactive for more than two months. Google allows Android mobile phone users to backup their device to Drive but these backups will be kept as long as you keep your device active.
If the device is unused for two weeks, Google Drive will then display an expiration date below the backup, showing a countdown of how much longer you have until it gets automatically wiped.
Presumably, if you use your Android device during this warning period, the delete notification will go away but after two consecutive months of inactivity, your backup will be automatically deleted.
If your backup gets deleted, you'll have no chance to restore it which means you will permanently lose valuable data and settings. But as long as you have one Android device checking into your Google servers at least once in every month, you can rest assured your backups will be intact.