Our daughter is a Ewings survivor (we are still in the 5 year slide). She also lost about 30% of her body weight and we had a really hard time. You can read about her at www.caringbridge.org/visit/mirandabeamer.
As for the necessity of the treatment, I can't answer that. There is evidence that stopping treatment after removal of the tumor is almost as effective as completing the full regimen, but that is after 6 rounds (or 3 cycles of 5 days and 3 days). There is no evidence that not having chemo at all is effective.
Ewings is very aggressive. If they truly got all of the cancer, you might get away with not treating. But, if they missed just a few cells, it could metastasize in the lungs and then the survival chance goes from close to 80% to less than 20%.
I wish there were easy answers. If there is one ray of hope, the survival rate for small children with Ewings is very high. For soft tissue tumors, it is 100%. BUT, there were only four in the seven years of study of the new regimen, which is not conclusive scientifically. But, it is something to hold onto during the long nights watching your child get sicker and sicker.
If it gets really bad, consider a G tube or GJ tube. It was a lifesaver for us. If you want to converse privately, it is gbworld (at) comcast.net.
Peace and Grace,
Greg