I saw a similar thread, but no definite answer that I can understand

I bought a ticket premium economy, united, SEA -> SFO -> PVG

I saw an upgrade waitlist opportunity for $450 dollars + 35K miles, that would upgrade the entire trip from premium economy to business

I did, and the united promptly charged that money to my credit card and deducted my mileage

Now, I got confirmed upgrade for the SEA->SFO, but is 9th place in the waitlist for the SFO->PVG

I really don't care about seating for the first leg. If the second leg upgrade fails, would I get the entire expenses ($450 + 35K miles) back automatically？ What happens to the first leg upgrade? Would united automatically put me back in economy plus? Or do I keep the upgrade? (that doesn't make sense as I would be getting a free upgrade from SEA->SFO?)

Different agent are giving me different wild answers...