If the man performed to her satisfaction Queen Rat would reward him with good luck. If not, or if he told anyone about her, he would lose it, die by drowning, or otherwise meet with an accident.
Although this sort of luck-bringing supernatural woman is common in folklore, Queen Rat is unusual in that there are no stories of descendants of these unions. Instead, the man's family is marked through the daughters of his human partner - one girl would be born with odd eyes and acute hearing. This is said to have happened though several generations of the tosher Jerry Sweetly, who on his deathbed told his grandson about his encounter with Queen Rat.