Sorry, sherrardk, you wanted to know what happened in the end. Johnny Spence returned & tried to kill his wife (after he saw her in bed with John Standing) with an overdose of Lady Spence's drugs.
John Standing followed him to the factory, they had a fight, and John killed Johnny Spence and pushed his body into one of the furnaces. Although he had done so much good within the Spence family, John had decided to leave the house to return to his former life. However, Lady Spence's companion/nurse persuaded him to stay so he did. She and the little girl were the only two who realised that he was not Johnny Spence.