What happens if h4 extension in USA is approved after F1 visa stamping in India?

I am appearing for my F1 visa interview in India on 30 July 2015 and my petition for H4 extention is pending with USCIS ( filled on 3 June 2015). What happens if my H4 petition is approved after my F1 visa interview and before i reach US and clear the port of entry?

My existing H4 visa is valid until 13 May 2016 and date on my I-94 is 22 May 2016.

Should i reschedule my F1 visa date and get husband’s H1B and my H4 filled in premium procesing? ( My school begins on 19th August 2015)