H4-F1 COS and F1 stamping in last semester

Hi all

I am Priya and doing my masters on H4-F1 COS. I will be graduating in Dec 17. I have to travel to India on an emergency, please help me to get answers for below questions-

  1. Do I need to get my H-4 restamped if the F-1 visa is rejected, my H-4 visa is valid till Aug 2019.

  2. Can I apply for COS again in Aug or Sep 2017, considering I will be graduating in Dec 2017, will there be any impact on my OPT.