Lawyers for Donald J. Trump and his co-defendants in Georgia could appeal a judge’s decision allowing Fani T. Willis, the Fulton County district attorney, to remain on the election interference case. But it will be up to the judge whether their appeal could go forward right away, or if it would have to wait until after a trial.

Ms. Willis could also choose to appeal the decision, though that is less likely since the judge is giving her the option of keeping control of the Trump case.

For an immediate appeal, the defense lawyers would ask the presiding trial judge, Scott McAfee of Fulton County Superior Court, to grant them a “certificate of immediate review.” This is essentially a permission slip that would allow them to take the case directly to the Georgia Court of Appeals.

If Judge McAfee gives his approval for an appeal, it would then be up to the appeals court to decide whether a panel of three appellate judges should take up the case. If the court grants this request, the prosecution of Mr. Trump and his allies could be suspended until the appeals process plays out, which could take months.

The appeals court also could speed up the process by deciding to put the case on an expedited schedule. That decision would be closely watched, given the fact that Mr. Trump is likely to be the Republican nominee in the November presidential election.

Mr. Trump, who has sought to delay all of his four pending criminal cases as much as possible, would likely be pleased if the appeals court decided to move at its normal slower pace.

If the defendants were to lose at the appeals court level, they could petition the Georgia Supreme Court to take up the case.

Steven Sadow, the main lawyer for Mr. Trump in the Georgia case, said on Friday morning that the defense would “use all legal options available” to continue to fight the case, strongly suggesting his team will try to appeal the order.