Vincent ducks the debris thrown at him, surprised by the speed it came at him. He withdraws to the best range he can still keep hold of the spell at. It forces him to divide his focus, but he casts an illusion spell at the same time, projecting a giant glowing 'A' into the sky above. If they were going to throw him out, then they could be the ones to handle this. Granted, he wasn't so callous that he was going to let the monster keep rampaging without hindrance, but he didn't want to have to deal with it by himself.