Users are reporting that Google has started slashing and burning old accounts in recent days, seemingly with no warning. The first sign something is wrong comes in the form of an alert sent to the user's backup email informing them their Google account has been deleted because of an unresolved terms of service violation. Whatever is going on, it's probably time to backup any unused accounts you have sitting around.
The Gmail support forums are packed with users reporting their old accounts have been nuked, and several Reddit threads have popped up in the last few days as well. Most affected users say the deleted accounts hadn't been used in a long time, possibly years. It's unlikely an inactive account could violate Google's terms of service. Even though the email claims users can restore the accounts if they act quickly, everyone is reporting that the deleted accounts are irrecoverable.
Google hasn't responded to requests from the support moderators, but I'd wager this is at least partially a mistake. It wouldn't be surprising if Google clears out free accounts that haven't been touched in years, but the ToS email and immediate deletion doesn't seem correct. A message that explains the situation and gives users a chance to stop the removal of their account would be a better approach.
We don't know what's going on yet. Maybe the deletions are supposed to be happening, but the alerts aren't being sent correctly. It's also possible this is just one big screw up and Google didn't intend to vaporize these accounts. In which case, yikes. We haven't seen anyone claiming their active account was deleted in this fashion, but still, you should always have a backup from Google Takeout. If you've got an old account that has something important on it, definitely save a copy locally.