The last application in is usually what USCIS will use to adjudicate your status. If your change of status form F-1 to F-2 is denied and then you make 30 days to depart and you then turn around to file another change of status say to B-2, most likely this will not be looked upon very favorably by USCIS and they may also deny this and deem you out of status unless you initial status F-1 was still valid than youre OK and do not have to leave.
I agree with my colleague.
(213) 394-4554 x0 Mr. Shusterman is a former INS Trial Attorney (1976-82) with over 35 years of immigration experience. His response to your question is general in nature, as not all the facts are known to him. You should retain an attorney experienced in immigration law to review all the facts in your case in order to receive advice specific to your case. Mr. Shusterman's statement above does not create an attorney/client relationship.