I've applied an SWU to a MEL-SYD-SFO flight on the 1st of February, 2009. It's cleared for the MEL-SYD portion, but not for SYD-SFO. If it clears before checkin then everything's fine, but what are the chances that the SYD-SFO portion will only clear at the gate at Sydney (if this is even possible)? I'm obviously not keen on burning an SWU for MEL-SYD alone, so given the choice I'd rather revert it at Melbourne - I can't see there being any shortage of space in economy for that leg.

So. In the worst case, can I revert back to economy at Melbourne and still remain waitlisted for SYD-SFO?

(I'm also waitlisted for SFO-SYD on the outbound leg, but LHR-SFO has cleared so I'm happy enough anyway. Even if it does mean old-style business. I've a stopover in SF on the way back, hence the asymmetry)