So much more stable it's not even funny. Alec and Viola would have married when she was in her early twenties instead of her late teens, and they would have gotten off to a much better start without the rift of Isabelle between them. Alec would still take subtle opportunities to corrupt Viola, and eventually would choose some other woman to bear a child they would pass off as Viola's. They would still be an evil power couple, but much more uncomplicated and more lovey dovey. Their major conflicts would be more moral and less personal, and Viola's morality is never as strong as her personal interests.