Thanks for the information. If Arth-Walchwil-Zug is out of service, I can simply extend my trip to Luzern and then to Zurich from there. I guess that there are also trains that stop at Rotkreuz where it should also be possible to change to the next Zurich bound train (from Luzern).
I will be travelling with a Rail Pass. I guess that I would still need a reservation for some trains.
What routes do I have the best chance to see or catch either a Twindexx or Giruno?