What does it mean when a text message says expired?
EXPIRED: Means that the handset may have been switched off or out of signal for a long period of time, and the networks validity of the message has expired. They do try to send the message to the mobile over a 24-48 hour period, after this time frame the message would have expired.
Can you set a text message to expire?
Tap Messages. Scroll down and select the Keep Messages option under the Message History heading. Choose for how long you would like to keep the messages on your iPhone: 30 Days, 1 Year, or Forever. Depending on your choice, you might be prompted to confirm it by tapping the Delete button.