That's certainly possible. Of all the West Coast routes, MKE-LAX could probably be sustained at 1x daily.

The yields on MKE-West Coast are horrible so fares will have to increase or Southwest will pull the plug and route passengers elsewhere. Without the intense competition and fire sale fares they might be able to make a go of it.

I'm still amazed that Frontier is walking away from LAX/SFO during the peak summer travel season. Even more interesting is that they are keeping SEA (which has AirTran competition at 2x daily) and SAN (where despite having a non-stop flight last year they still managed to have a lower fare than one-stop or connecting options on other carriers). Personally I thought Frontier might reduce LAX and SFO to say, 4 times per week, instead of outright cancellation.