What happens if the Supreme Court rules like this?

[SteveRogers]

This happens from time to time. There wouldn't be a true majority opinion. You would generally end up with an opinion joined by four justices "announcing the judgment of the court," an opinion "concurring in the judgment of the court" by the swing justice, and then dissent(s) by the other four justices.

As others have said, there wouldn't be a true precedent set. Lawyers would spend years afterwards arguing what the narrowest holding that five justices actually agreed on was, and when the issue came up again lawyers on both sides would argue about which plurality was more persuasive.

Off the top of my head, Vieth v. Jubelirer was something like what you're talking about. 4 justices agreed that partisan gerrymandering claims are nonjusticiable, 4 justices agreed that there are judicially manageable standards for policing partisan gerrymandering, and Kennedy wrote his own opinion agreeing with the majority that this particular case was nonjusticiable but holding out hope that the court might one day create a workable test for partisan gerrymandering claims. So the issue got kicked down the road without a clear precedent.