Yes, of course there would have been no difference since the law states that labor groups represented by the same union still have to use that union's procedures.
Had the law been in effect and either east or west been successful in previous years in their attempts to dump ALPA, the outcome would likely have been very different on several levels.
First, if it had gotten to arbitration, there would have been no vague, ambiguous ALPA merger policy to deal with. The arbitrator would have had his/her wits (those that are still young enough to have wits, that is) and decades of precedent to fall back on. And the law specifies Allegheny-Mohawk as the starting point (which was a DOH merger.)