which service center did u apply? If you applied in california, then I am not sure if you will have your extension approved by august. For other service center, you have a better chance.
Keep checking the processing times and H1 tracker thread.
You can comeback in your existing H1 visa as long as it has not expired. Dont comeback unless you are absolutely sure that your extension was not going to be approved till you comeback to the USA. If it gets approved while you are in India, then wait in India and get the approval notice mailed to you and get a new H1 visa. Or, if you have unexpired visa, you can enter using that visa but you can get I-94 based on the extension approval notice.