There's some you'd lose. I know you'd lose the trophy you get for rating over 50% of story games, as I used to have that and have since lost it. Other things like Top Poster trophies would be lost if other people overtook you, and the Lucky Dueler trophy which can only be owned by one person (it's mine, you can't have it!) I'm not sure about featured storygame trophies though. If you have a game that gets featured and at some point your game in taken from the list of featured games and replaced with another, I think you still keep the featured game trophy, but again, I'm not really sure.