In a workshop environment a freewheel rebuild is not that bad, though it is time consuming and may not be worth the expense given the current cost of entry level freewheels.

However, Stacey's comment reminded me a terrible experience I had about 25 years ago. I was participating in an autumn Century tour that was cold and wet, when a friend's freewheel dissasembled itself. There we were, miles from nowhere, kneeling on the road, with near frozen fingers, trying to find and pick the ball bearings out of the ripples in the asphalt. The passing car drivers would slow down and roll down the windows to see what was going on. A few laughed at our predicament. It was very frustrating that none offered to transport my friend and her disabled bicycle to the nearest town. Somehow we managed to find enough bearings and get the freewheel assembled. I used a rock as a hammer and took apart my chain tool, permitting me to use the pin as a punch to tighten the cover plate. It seemd like we were out there for hours. Fortunately the roadside repair held up. It's not an experience that I don't want to go through again.