You will not lose no change fee, but there's no guarantee flight price will still be same on new flights (due to bucket class inventory availability, seasonality requirements, etc). In particular, you will need to find flights with V bucket inventory since that is what you originally booked. DL currently has no change fees on ex-US Main Cabin or higher fares (when you purchase a roundtrip ex-US, both outbound and return will use US origin fare filings and be subject to same fare rules/change fees). Once outbound has been flown, they can generally use your original ticket issue date to measure advance purchase requirement on fares for return flights (whereas booking a new fare on same flights may not qualify for cheaper advance purchase fares if it is too close-in to meet them) and they can often keep your original fare as long as original booking class inventory is available on new flights (although you may be subject to higher fares due to other issues like seasonality requirements or day of travel requirements on certain cheaper fares). I'm not seeing fares with seasonality requirements right now on cheaper ORD-PVG fares, but V fares for Fri-Mon returns (VNW0ZPMU) are currently $50 higher than Tue-Thu return V fares (VNX0ZPMU).

Also, you will be eligible for roundtrip fares for return flight as it is part of roundtrip itin while attempting to book a new one-way will only allow you to book one-way fares which will generally cost more (although there are some nuances here as attempting to book a new one way ex-China will quote ex-China fares which are different from ex-US fares which is what you are currently booked on).