Needless to say, when Mavis gets frozen, Zeref's going to react very, very badly. However, due to the nature of his curse, he'll have to control his reaction very strictly.

He would become hell-bent on what caused all of this, and end it, including violently if necessary. If that sounds callous, it is; he can't allow himself to give much thought to Mavis' safety, or else he'll be the one jeopardizing it. But deep down, anyone would be able to see that he's extremely distraught, and worried, even if he will do everything in his power to deny it.

When the time comes for storming the castle, he's in.