Question? About ducklings?

two ducklings hatch good friends. Last duckling hatched. He imprinted on me, followed me around,crys when i leave. the ducklings were pecking him but now finally they are acting like good friends. When I walk away and he is with the other ducklings he doesn't follow, well he does when he is out alone and the other ducklings are in the brooder. I was just wondering if this means he won't think I am his mother anymore, or once they imprint do they always think your their mother even if they become friends with other ducklings or will he forget he imprinted on me? The others like me but didn't imprint on me so they don't follow me. Only he imprinted on me but because they are friends I feel he will forget he did. Can he?