Im no expert and there might be a better way, but some random suggestions to make sure you get at least something without a total loss: take a screen shot of each message using the sleep/home button combo or copy and paste each message to email and then email them to yourself or if you have iMessage on your computer there may be a library/data file with those messages...good luck.
That would literally take years. I send over 1.000 messages per day lol