Recover deleted imessages from IPad
How do I recover deleted imessages from an Ipad?
iPad Pro 9.7-inch WiFi
if you were syncing them to icloud then it gone as outlined here Keep all your messages in iCloud - Apple Support
If you weren't syncing to icloud and you backed up your device as outlined here How to back up your iPhone, iPad, and iPod touch - Apple Support
The you would need to do this Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
IF you didn't back up then the message is gone.