Instead of the Avengers helping the Maximoff twins to escape, they do it on their own. The two later join the Avengers, helping them slowly bring down Hydra, so they wouldn't hurt anyone anymore.
In the process of doing so, Natasha and Wanda fell in love. And as life had to have it, tragedy struck and Hydra managed to kidnaped Wanda during on of their attacks.
Now the Avengers had a new goal, get her back before they gained too much control over her. But when they reached her, it already seemed too late.
(Scarletwidow FF)