Should you have an account that is about to be deleted, you would think that you would first receive some type of warning as to the reasons for the action, or that it was about to happen. According to numerous postings across various social forums multiple users are reporting that Google has deleted their accounts without any warning that the account deletion would be taking place, but stating the reason was due to a violation of the terms of service which hadn't been resolved. It's also worth noting that this seems to be happening to people with older accounts which are rarely used or completely unused and doesn't seem to be happening to people who have active accounts which are interacted with on a regular basis.
In what would be some light at the end of the tunnel for those who have received such emails about these accounts being taken down, Google has stated that taking some form of immediate action would allow users to restore these accounts. However, users who have tried this are also reporting that the attempts to restore deleted accounts was to no avail with a returned message that stated "This account was deleted and is no longer recoverable." So far there hasn't ben any word from Google on the issue at hand which leaves everyone without a definitive explanation as to why this is happening.
If you have an old Google account which you barely touch or haven't used in quite some time, it would be advantageous to make sure you save or backup anything you don't want to lose. If you want to take precautionary measures and make a backup archive of all of your data, you can do so by hitting this link to take you directly the page to which allows you to start the process. As stated above it doesn't appear that Google is wiping out primary active accounts, but it's better to be safe than sorry and make sure you have all of your account data safe and sound. If you've already received one of these emails for an older account, heading over to the Google Product Forums to create a post about the issue could perhaps gain you some assistance with recovery.