kb1992My understanding is:
BOS-ORD XF Waitlisted
ORD-PVG XC Confirmed
PVG-ORD XC waitlisted
ORD-BOS XF waitlisted
Yes, you will fly in Y if waitlist does not clear.
Since you paid with 90,000 miles for a saver C award, your waitlist will go to FFCC at check-in. If there is any open C seat available PVG-ORD and F seat available for the domestic portion in a two-class service, you will be processed prior to any upgrade.
I have done this many times with 100% success.