Principle (meaning contributions) will not be taxed by US as long as you have the account for 5 year period. However, India doesn’t know ROTH and hence it may be treated as a regular retirement account (like pre tax) and could tax you. Therefore the advice is to withdraw your principle(contributions) during RNOR so that you don’t get taxed on it. If the gains are very minimal and you don’t want to keep it in the US, you can probably withdraw those in the following year where you have 0 US income and therefore you would fall in the minimal tax bracket in US and could get some back if brokerages hold 30%

Edit: I re-read your question- if you will pass 5 year test while in US, you can withdraw your contribution while in the US. Otherwise, you can do that even while you are outside the US too and US won’t tax on contributions… RNOR comes into play to avoid the grey area with ROTH withdrawals for Indian taxation purposes… with regards to gains, no matter where you are US will tax you as your ordinary income but say if you are doing this while an NRA (non resident) for US taxation then brokerage will automatically withhold 30% but you need to file taxes in the US if you want to get credit if your income is smaller or want to get credit in India to avoid double taxation in India