Sorry, but I call BS on these being lost. There are many ways to retrieve the messages.
First, the messages are between two of more parties, so each party involved is subject to have access to the message.
Second, the physical devices themselves would/could have the messages still on them.
Third, most wireless carriers store text messages for up to five years and they can be subpoenaed.
Fourth, depending on the device, they may be accessible in another server such as iCloud for Apple devices or BES servers for Blackberry.
Finally, if they used a third party text messaging app like Google Messages or Facebook Messenger (both of which can replace the default device messenger app), there is another way they can be accessed. For example, I can see all text messages on my personal main phone on both tablets, my PC, and my other phone because of the messenger app I use.
