you wiill lose F1 staus when you enter using AP. And you can't apply for f1 due to your obvious immigration intention. But it is fine. You can stay in this country freely with your 485 pending status to finish your study. Actually you are gaining more freedom as you don't need to be restricted as a F1 student. The only thing is, you need to apply for EAD if you still want to work as RA/TA therefore you can get paid legally.
So if your 140 has been approved, don't worry about that. Just apply for EAD now. You should be able to get that by the time you come back to US.
But if your 140 is still pending and you have a weak case, you have to re-consider your choice. Once your 485 is denied, you have to leave this country.
Good luck.