Frequently Asked Questions - F-2 Visa
You must be married to the F-1 holder in order to be eligible for F-2 status. Fiances do not qualify for derivative status.
You will need a new visa only if you return after August 2013. Check with your DSO to make sure you have all the appropriate requirements completed.
If you are subject to H-1 quota, to get status within USA, you must maintain status till September 30. So, it appears you may have to apply for H-4 as well as H-1. Your lawyers can help you figure out the timing. Applying for H-4 now should not be an issue. But move quickly. You can file for H-4 online. Fairly easy.