WordPress.com users with expired domains seem to be the flavor du jour in the Community forums today. So, this would be a good opportunity to remind users that if you’ve registered a domain name, regardless of whether through WordPress.com or not, take a moment and go look up your domain’s expiration date and add it to your calendar, digital or otherwise. If you registered your domain through WordPress.com, you can find this information in the “My Purchases” section of your Dashboard and if your domain is registered elsewhere, you can find it with your Domain Registrar or by performing a WHOIS search on your domain. Don’t depend solely on a renewal reminder notice or email from your domain registrar to keep your domain name up to date and in your possession.
Also, even if you’ve set your domain to automatically renew, check that your chosen payment method is current and that the renewal takes place on time. Don’t just assume it will.
If you don’t, you may find that recovering an expired domain could get very costly.
WordPress.com explains the Domain Expiration Process