I'm not sure what you're trying to theorize, but it's clearly a fact that a subpoena or a search warrant is meaningless when served on a party that doesn't possess (or have the ability to possess) what LE is trying to obtain. For example, you could get a subpoena or search warrant for the Titanic on my property, but it's not doing you any good even if you get it.
Of course, one of the elements for a sw is for LE to demonstrate a likelihood that the search will produce what's being searched for, so given the fact that Apple won't have the info, a court would probably refuse such a quixotic request if asked.
But even if they got past that hurdle, if Apple doesn't have any ability to access customer password-protected info, all the court orders in the world allowing LE to force such info from Apple won't matter.