If you have to go back to school and get paid as RA/TA again for at least one more semester after your internship, then you have to deal with ISO then. You HAVE to let them know that you are no longer F1, and you need a new I-9 with the payroll and u can only receive payment with your EAD.
From the INS standpoint, any illegal work will prevent you from getting your green card.
And the bottom line is, you can't keep your F1 and work with EAD at the same time. It is AGAINST the LAW.
Decide for yourself but beware of the consequences.