I have seen and have had horses with bows. One of my OTTBs has an old bow and raced on it for years after he recovered! A bow is a bow, no matter how slight someone might say it is. High bows are easier to recover then low bows, but both are recoverable unless the tendon was severed. I would ask more questions regarding the bow. The scaring would only be in the inside tissue of the leg, if it has healed completely, you will not see any scaring on the outside. The amount of time off you give a horse depends on the severely the horse bowed. I wouldn't rule out jumping a horse with an old bow, many of them recover and do just find in the jumping ring, those are called "proven bows". You can never out rule that the horse will never re-bow again, just like you can never out-rule that a horse will never bow in the first place. You can also have a vet do an Ultrasound on that leg and see how well the tissue has healed itself!