Depends on the horse. My horse is very good and won't rub out braids overnight or so. But my friends will rub the braids out within an hour
Not all horses but a majority
Every horse I've known dubbed their braids out of not wrapped. But braids should not be left in for extended periods of time.
Not necessarily but you should never leave a braid in for more than 24 hours. If the braid is out and their still rubbing their tail maybe clean the sheath