I'm not sure that this would be all that likely a result. Contrary to what rumors about Big 10 schools adding hockey often entail it is not mandatory that a sport with six Big 10 teams must become a conference sport. That's the point at which it is allowed but it is not required.
With men's hockey the Big 10 jumped when Penn State added a varsity team because the Big 10 Network wanted more programming and would rather feature two Big 10 teams playing each other than games against out-of-conference opponents. I don't see any indication that BTN is hungry to add more women's hockey to their lineup, so that pressure doesn't exist. It would strictly be a question of the prestige of adding the sport versus the additional travel costs that would be incurred. I think there's a pretty good chance, though not a certainty, that the latter would prevail and the existing leagues would continue.
Take the scenario that the rumored upgrade of Michigan's club team to varsity status comes to pass. I'd bet money that any such announcement would be followed by Michigan State doing the same; if one adds it, the other will, too. That would mean that there are six Big 10 teams and the league could add the sport. Equally likely, I think, is that Michigan and Michigan State would just join the CHA, bringing it to eight teams. If so, Ohio State would probably leave the WCHA to play teams that are closer as well as its most natural rivals. Perhaps there would be a trade and Lindenwood would move to the WCHA, as that makes more geographic sense.