Granny Numa freed them from that telekinetic grip, because she got what she wanted. One would use this opportunity to escape, but they knew that it would be useless to run right now.
They had to use this freedom cleverly, especially since their first plan failed so miserably. Chances are that Numa employed them for this 'witch hunt' from the very beginning, she knew what a 'pure necromancer' was capable of, and yearned for these sour results about her island!
Bardeelus remained calm nonetheless, and sought for ways to negotiate a deal on behalf of the whole team! He felt invincible, or at least, he knew that he could kill each and every one of these telekinetic mages if it got to that point. He had to look for safer alternatives, because if he couldn't come up with a quick solution, then no one could!