Regarding the success rate, i think they approve in most cases. I know few years back, they rejected the appeal of a guy who had dropped a class at the middle of the semester thus failing to maintain required minimum units. Instead of giving him re-instatement, they issued him a letter urging him either to voluntarily depart from US within 30 days or face the removal by themselves. I guess there may have been some other reasons behind that decision e.g., poor performance in the classes he completed and or not being registered on time for the following semester etc. I think that was the most severe case. Normally, it should not happen. It also depends on how they take your case and how you present the circumstances behind the inability to maintain staus. If you can show some health reason with substantial proof, it will be excellent i think. The above case i mentioned was just for an example (a true story though). You should be okay. Just complete your process cautiously.