In one respect, the Ewells' lives would not have changed very much. They were completely ostracized before, and that would have continued, except the citizens of Maycomb with a few exceptions would have held them in even deeper contempt for Mayella's behavior.
The consequences for Mayella, however, most likely would have been severe, even fatal. Her father had beaten her when he saw her behavior with Tom Robinson. One can only imagine what Bob Ewell would have done to his daughter if her behavior had been established without doubt in Maycomb. His rage and shame would have been overwhelming; he might have beaten Mayella to death the next time. This is not hard to imagine considering Bob Ewell's behavior after the trial even when Tom Robinson had been found guilty. He spit in Atticus' face in public, but even that was not enough to vent his anger. He later tried to kill Atticus' children.
The consequences socially would be dramatic for a time, and then, I think they would wear off. Bob, if no legal consequence for him was pursued, would have trouble facing anyone in town, but he would have been used to that. The shame that people typically had for the Ewells up until this point had to do with his drinking and living off the welfare of the county. Now, a moral injustice would compound people's ill will for him and his family.
If further investigation into the perjury of both Bob and Mayella's testimonies were pursued, Bob might have ended up in jail. Mayella may have been found out that her lies were coerced and a lesser penalty could have been given to her. If she told the truth, the state would have likely placed extra care for the children and help for Mayella. Because of that little row of flowers, I think Mayella wanted to be better than she was and I think she was willing to work for it. Given the absence of her father and the opportunity, she just might make something of herself. She could have earned a job and sent those kids off to school every day. The shame of trying to defame Tom Robinson would have likely worn off quickly because after all, he was a Negro, and the town would not have cared too much about his feelings or the fact that he was wronged.