I have never had a bike fail off road due to any water cooling problems. That's because my off road bikes are, and will be, air cooled. One less thing to ball up when you're 50 miles from nowhere in the desert.
And, funny thing, when I go out in the desert with my friends my old air cooled DR400 gets to the destination at the same time as the guys on the latest and greatest wunderbikes. Hmmmm. Same thing happens when I'm on the road for that matter. What was that wonderful advantage again?