Deleted messages

you might have a chance to retrieve them from your Google back up if it hasnt re updated yet but usually if you delete a message or text thread its gone for good unfortunately.

sign into Google and see if you can find when the last time it was that it backed up your phones info..

Does tmobile keep a record of deleted text message content if it was deleted if it is still in the time period? 

No, all they keep is numbers.