He won't be allowed to do anything without an attorney. The judge will let you present your case, even call the person to the stand and force him to answer questions under oath, if you need. But, the person will not be allowed to do a single thing in defense of the corporation without an attorney.
If the hearing is on the motion to dismiss and he shows up without an attorney, he will lose the motion. Also, having been warned, the judge might order sanctions against the man for wasting your and your attorney's time (assuming you are represented).
Please let me know, if you have follow-up questions.
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