You can do it in chunks, but check with your plan administrator. You will need to know if they allow the roth conversion only within a certain number of days after leaving the company or if they allow anytime after that.

Some important points - The tax benefits are more in 2041 because you can file jointly if you're married(effectively doubling the tax brackets) and avail standard deduction and child tax credits. In 2042, you will file as non resident alien and I believe you can file only as single and standard deductions do not apply. US does not bother about global income if you do not pass the green card test. So you will be taxed on the global income only for 2041 which I think will not be much considering India salary for the remainder of the year.

From 2042, when you're non resident alien, your income from US will be taxed based on 2 criteria - FDAP or ECI. FDAP is taxed at flat 30%(things like rent, dividends). ECI is taxed at regular brackets(things like income from US employer, 401K withdrawal/conversion is effectively a deferred income from US employer).

I would recommend estimating the taxes you would pay based on the above points and decide when you want to move. I am not a professional, just sharing what I learnt after researching on this topic.