In theory, any number of schools could've plucked Ara and Dan, as well as Lou, before ND did. Lou's OSU opportunity was tangible and non-speculative, but there always has to be some element of fortuity present for an elite coach to be available for hire.
What matters is how the school capitalizes on its good fortune. Michigan took full advantage with respect to Harbaugh. As noted below by Bruno, today's Notre Dame likely would've squandered the same opportunity through the same lethal combination of hubris and incompetence that has held us down for the last two decades.