What phone do you have? Does it have a back up facility that may have stored the text? What network is it on? I''m on o2 and they provide an online chat service on their website. Might be worth looking to see if your provider does and see if there is anything they can do.
If its an iPhone, there are ways to recover it, as it may dissapear from you messaging app, the hard drive on your phone stores it. There are companies that can recover for you too. If you are a techie you can probably do it yourself. Be ware of free tools online though, they are never quite free!