No. Oral argument to an appellate court is voluntary for the parties unless requested by the court. That hardly ever happens. In fact, the courts often encourage parties to waive oral argument and there is chronic debate within the appellate bar as to whether oral argument has much impact in most cases.
In all events, the court will not hold open the argument stage of the appeal pending transcription of the opposing party's argument, review of that by you, and the submission of a response argument by you. All that is what the briefing was for.
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Appearing at the oral argument is your opportunity to "reply". Once oral argument takes place the matter will then be taken under submission and a decision made. You do not get an opportunity to reply to the oral argument by submission of a written reply. The defendant's request for oral argument will not be denied. If you can't afford to come here for the oral argument, why not hire an appellate attorney for the limited purpose of appearing at the oral argument.