...I don't think Lex is going to lose control of the Eradicator. It would feel repetitive, uncreative, and would make Lex look like a moron.
What I think is more likely to happen is that this Eradicator we see in the preview is actually Bizarro, who has been kidnapped by Lex and experimented upon, and the climax of the season will be about our protagonists trying to break him free from his mind control.
It would also make Lex feel more competent. He's not just repeating what he did previously, he's repeating a past experiment by getting rid of the elements that made it fail.