Different people have suggested different things as to what constitutes, "the unitary executive theory". The US Supreme Court is not likely to simply adopt such a theory in general terms. It will, instead, rule on a specific case that comes before it, and state the principles behind that ruling.
There are a number of Supreme Court rulings saying that a President must abide by laws limiting presidential authority, perhaps the most famous is Youngstown Sheet & Tube Co. v. Sawyer, 343 U.S. 579 (1952) in which the Court rules that the President did not have authority to seize steel mills to put a stop to a labor dispute that was allegedly endangering national security during the Korean War. Congress had passed a law providing a different method of dealing with such situations, and President Truman did not follow the method established by that law.
The President has broad power over the operations of executive branch agencies, possibly including the right to order an investigation halted for whatever reasons seem good to the president. If such a case came before the courts and they supported the President, presumably they would hold that the President's actions did not constitute obstruction of justice or any other crime.
I find it highly unlikely that the Supreme Court would rule that the President may "act against the rule of law", but they might rule that in particular cases the law implicitly grants the President power to take certain actions that others may not take.