Urgent questions: Would existing visa still be considered valid

I have an urgent question regarding my parents’ application for a B-2 visa to the US. I would really appreciate if you can help me with an answer.

My parents have their existing B-2 visa that is going to expire on 11/8/06. They are planning to visit US Consulate in China to re-apply for another visa so that they can come visit in Jan 07. If their application for the new visa gets rejected, can they still use their existing visa to come visit prior to its expiration date, say 10/31/06? Would my parents' existing visa still be considered valid if they are being rejected prior to its expiration?

Looking forward to your comment.