No backup camera? I know you want light but have one little failure and you are out of commission.... It's not like you can pop into a store and pickup a medium format camera....
I know Colin Fletcher was able to provision a Contaflex from the bottom of the Grand Canyon in the middle of a trip, but he was a writer not a photographer.
Do you own another MF camera you can throw in the back in a "first-aid kid" kind of box that you only open in an emergency... Then the camera won't distract you but will "be there" if you need it.
Since you're already provisioned, doesn't make sense to argue that you should bring only one film. You'll have to make sure you have the right film in the camera at the right time. For example in the morning, if you still have last night's 400 loaded, you might unload and reload with 100 for the day (even if you are in the middle of a roll). If you leave 400 in during the day, you might take some fine landscapes that you won't be able to enlarge "as much" as you could have.