I've got 7,000+ miles of loaded tours on a XT 770 hub, and plan on riding it until I wear it out. One 3,000 mile tour had over 400 miles of dirt and unsurfaced roads and trails, and over 500 miles of cobble stones roads and trails. All withiout a problem.

My point is that I would not worry about it. I have another set of wheels with LX hubs, but I still plan on using the XT wheels for a 1000 mile tour next month. I'm not sure exactly how a free hub could fail "catastrophically". However, I could see how they could fail inconveniently.