Are the rewards lost if the trophies dropped?

No, once unlocked it remains unlocked, even when dropping below their mark.

Ok, thanks!!


Which score is used to determine your average for the tier you play next Conquest? Your final score or your high water mark?

Your final score. And next one is calculated by all three conquests, if this one is finished. Last 3 conquest results (final scores) count. 

Thank you.