I797, Visa Validity Question

[vandana716]

My visa is under 221g for client letter. I am going to drop the client letter along with my passport very soon. What will be the validity date of my Visa if I get stamped as my I797 is going to be expired on 30th September 2008.

Is there any chances of getting visa above the validity period of I797,LCA.

What should I do if they give visa in the last week of September 2008.

Please explain..