There is a reason why we send multiple notfications that your domain's expiration is coming up.  It is because reactivating a domain AFTER it has expired can be difficult. It can also be expensive, and in some cases it is not possible at all. First, a few definitions.

EXPIRATION DATE: The date your domain's registration period ends.

• A one year registration started on Jan 1st would have an expiration of Dec 31st of the same year.

RENEWAL GRACE PERIOD: The brief period of time AFTER EXPIRATION in which you may retrieve your domain at normal prices without penalty.

• All domains have a grace period after expiration. Currently, most domains registered through Monterey Bay Design have a grace period of 16 days. This value is subject to change.

REDEMPTION GRACE PERIOD: A period of usually 30 days at the end of the Renewal Grace Period.

• In this period, the domain is queued for deletion. Redemption of the domain during this time is a costly, time consuming, manual process. If the domain is not redeemed during this period, it will quickly pass through the PENDING DELETE period after which it will fall back into the publicly accessible names available for a fresh registration.
• If a backorder exists for this domain name, it will not be possible to retrieve it during the redemption period.

Retrieving a domain from the final redemption period is normally between $150 and $200.

Registrants' Benefits and Responsibilities: https://www.icann.org/resources/pages/benefits-2013-09-16-en
Registrants' Educational Materials: https://www.icann.org/resources/pages/educational-2012-02-25-en