i am not an expert.  but i believe once you file the change of status from H1 to F2 and get receipt before your employer terminates your H1B, you will be fine. 

I think so too. Once you file, USCIS will send you a receipt. Once you get the receipt, you are covered from the day receipt is issued to the day decision is made. If they approve your application, you are fine, if they don't then they will give you two choices either you refile and submit more documents or leave US within certain days.