It always surprises me that so many people think when you delete your photos or texts that they are "gone forever".
If you backed up your phone to iCloud or iTunes you can retrieve the messages.
If you're not sure if you backed it up or not, you can search for messages by going to > Settings >General>Spotlight Search>Messages to check it, then search for the message (if you can remember a odd word or phrase from the text).
And if you ever lose a really, really important text, a data retrieval agency might help (for a big price).
On the very small chance that you are asking (or people read this) because you (they) want to check on someone's text messages and/or see if they are deleting text messages, you can do two things:
1. Check your bill to see who is being texted and when, and how many texts are received/sent.
2. mobile-spy dot com monitors people's texts, but it has to be downloaded on the person's phone (good for an employee or a child).