Question about reinstatement

I am trying to get back to F1 status after OPT - I haven't finished my degree yet so I am going back to the same school and program. I filed i-539 and now waiting for their decision.

Question: what if I got rejected? Will they give me sometime to leave the country? Can i apply for F1 again after i go back to China? Anybody knows or have the experience how it works?

Thanks!