I have the exact same thing going on. I deleted a character without realizing it was holding the exotic kinetic item. Now I'm permanently at step 3/4, with no way to present the purified mementos to the statue in exchange for the bow. This sucks. I've checked every vendor. I've dropped the quest and reacquired it. I've deleted characters and started a totally fresh one, but the quest is account-wide so it's impossible to start back from zero. I've run that damn dungeon way too many times.