U have graduated,Ur Visa has expired,U already got an OPT..So where does this I-20 comes in picture..of course u will still be in f-1 status , but i don't think u can get new f1 visa stamped into ur passport..based on I20...talk with ur employer and try to get some other category of visa..u said u have been offerd job from a school so why don't u try for h1b visa if they sponsor..u won't have to go through the quota and it can be granted any time..