You can read the 60-page response here. The plaintiffs do not address the Purcell principle question until the very end of the brief, where they say:

Finally, Purcell v. Gonzalez, 549 U.S. 1 (2006), does not, as Applicants suggest, Motion at 13, instruct lower courts to categorically “avoid” ordering changes to upcoming elections. In Purcell, plaintiffs challenged a new Arizona voter identification law in an election year. Id. at 2-3. The district court denied the plaintiffs’ motion for a preliminary injunction that had been filed on the heels of the complaint. Id. at 3. After the plaintiffs appealed, and a month before the general election, the Ninth Circuit entered an injunction pending appeal without providing any explanation or rationale for its decision. Id. The Court ultimately upheld the district court’s judgment and chastised the Court of Appeals for its failure to “give deference to the discretion of the District Court.” Id. at 4-5. It was on this “procedural” basis—in a case that did not involve redistricting—that the Court struck down the Court of Appeals’ injunction. Id. Here, by contrast, Respondents filed suit three years before the 2016 General Election, and the district court found in Respondents’ favor on the merits after a full trial and thereafter denied Applicants’ motion to stay pending appeal. Applicants’ attempt to sidestep the careful, reasoned judgment of the district court, accordingly, finds no support in Purcell. In any event, Purcell merely reiterates in dicta what is not in dispute: “Court orders affecting elections, especially conflicting orders, can themselves result in voter confusion and consequent incentive to remain away from the polls.” 549 U.S. at 4-5. Respondents do not disagree. But the “public interest” is merely one factor relevant to whether a stay pending appeal should be granted, and—as the district court  found—other, weightier public interest considerations cut sharply against Applicants. ECF No. 148 at 4. Any confusion that may result from modifications to the primary election here is greatly outweighed by the constitutional injury suffered by millions of North Carolina citizens—and indeed the justifiable confusion these voters would face if they were forced to vote a third time in unconstitutional districts. One can hardly imagine a greater “incentive to remain away from the polls” than the knowledge that the election itself is unlawful. See id. at 5. Indeed, like the threat of voter fraud, racial gerrymandering undermines “[c]onfidence in the integrity of our electoral processes,” “drives honest citizens out of the democratic process,” and “breeds distrust of our government.” Id. at 4. Here, Applicants assert no interest in the “integrity of our electoral processes,” only in avoiding the administrative inconvenience of running a constitutional election. Unlike in Purcell, the Court is not considering a motion for preliminary injunctive relief filed in advance of an imminent general election. Compare 549 U.S. at 2-3. Rather, the district court issued a final judgment nine months before the 2016 General Election. The primary election date can and should be moved as necessary to allow for implementation of a remedial plan, as has been done repeatedly in North Carolina and other jurisdictions—and as legislators expressly contemplated would be done in the event the district court ruled in Respondents’ favor.28 Thus, the public interest factor weighs against Applicants here, notwithstanding the proximity of the primary election, and nothing in Purcell displaces consideration of the other stay factors—all of which also weigh strongly against Applicants here. The fact that the Purcell Court “recognized that practical considerations sometimes require courts to allow elections to proceed despite pending legal challenge,” Riley v. Kennedy, 553 U.S. 406, 426 (2008) (citing Purcell, 549 U.S. at 5-6), does not mean a losing litigant with little chance of success on the merits of an appeal is entitled to squeeze in one last illegal election as a matter of course. Simply put, a choice between forcing millions of North Carolinians to vote in yet another election under the unconstitutional enacted plan and taking the administrative steps necessary to hold a constitutional election in 2016—including delaying the congressional primary election as necessary—is no choice at all. See, e.g., Dye v. McKeithen, 856 F. Supp. 303, 306 (W.D. La. 1994) (“The potential injury of an election in which citizens are deprived of their right to vote negates any damage that may be sustained by Vernon Parish in the potential delay of elections.”).

I would expect a Court ruling within a few days, but we might never know if Justice Scalia’s absence would have any effect on the outcome.