" NRE accounts should be redesignated as resident rupee accounts or as RFC accounts (if eligible), at the option of the account holder immediately upon the return of the account holder to India if authorised dealer is satisfied that he has returned to India for taking up employment or for carrying on a business or vocation or for any other purpose with the intention of residing in India for an uncertain period."
As per income tax as soon as you lose NRI status, the interest shall become taxable at normal tax rates.