So, I have a red-eye SFO-ORD tonight which prompted for volunteers at check-in. I'm connecting to a trip ORD-IAD-ZRH-BOM which is also booked with UA but on a separate PNR (I booked this before moving from ORD to SFO, cheaper to buy surrounding flight than pay change fee/fare difference) with about 4 hours in between. Looking at SFO-ORD flights for late tonight/early tomorrow, they all seem pretty full (F=0, Y = 5 or fewer). If they do end up needing volunteers for my flight, would they be willing/able to combine the PNRs and bump me to some routing that gets me to IAD? How desperate would they have to be to consider this? :P