it will not stop forever
If you stop your baseball swing in the middle and the ball is not in the strike zone, an umpire will look at your wrists. If your wrists are "broken" it is a strike. That means the position of your wrists determine if you took a swing or not. If they are still in the same position as they normally are before you take a swing, you did not swing. If your wrists are in the position they would be in after you took a swing, you took a swing.
because they did
DK King of Swing happened in 2005.
Swing - video game - happened in 1997.
Swing Away Golf happened in 2000.
You can stop coming over the top in golf swing by doing a lot of practice.
It would oscillate faster.
Swing Away Golf was created on 2000-03-23.
gravity
Depends on where you're hurt at, of course.
Friction of air normally called drag (or air resistance), it could be argued that gravity also takes effect in stopping the swing, if it was only drag the swing could stop ten feet in the air, and if it was just gravity it wouldn't stop due to the laws of mass and momentum. The drag reduces the momentum, therefore making the swing slow to a stop and gravity keeps it as close to the ground as possible.