am flying LAX to LHR tomorrow via SFO (best flight times for me).

booked appropriate booking class to be able to upgrade with miles. LAX - SFO sector (which frankly I don't care about) cleared weeks ago but SFO - LHR sector hasn't clared.

shows 8 C seats available so am hoping I still got a chance to clear at the gate.

question though: my 30k miles got deducted which I guess is normal (and assume would be returned if I didnt clear). what happens though if I just don't clear for the SFO - LHR sector? are they keeping all 30k? or 15k for a domestic upgrade (which I'd rather not spend, i.e. if I somehow knew in LA (which I guess I won't) that I won't clear in SFO, I'd rather 'save the 15k and fly E+ to SFO from LAX.

thanks.