What happens to my NRE and NRO accounts on the day I permanently move back to India?

When you return to India for good and become a resident again under FEMA, you must redesignate your NRE and NRO accounts as resident accounts, or move the funds into an RFC (Resident Foreign Currency) account if you want to keep holding foreign currency. You can't keep operating NRE/NRO accounts as a resident. The RFC account is valuable because it lets a returning NRI park repatriated foreign earnings in dollars, earn interest, and later re-remit abroad without restriction, which is useful if there's any chance you'll move overseas again. Notify your banks promptly on return. Also revisit your US filing status, since your US tax residency and reporting obligations change in the year you leave.