A failed roll always brings down the player
So, why not, make things more interesting, they took all this time to describe the action to you, why not allow them to miss in the same grand way they would if they suceeded in their roll, but saying something along the lines of, "Well you didn't hit, but please describe what happens in your attack" or "You missed, but please tell me exactly how you missed". This will leave the player with a sense of accomplishment, while not bringing him or her out of the game mood. Best of all, you still get your miss! HA!