What happens if you...
 

Set waypoints for a ship, at 10 knots, and change it so it doesn't delete on last waypoint. Will it just sail on it's current course? I heard something about setting the last waypoint to zero to stop the ship, but what if you don't?

Ship will just stop at the last point and stay there. I'm sure it will move if attacked, but then it'll just go back to sitting there. If the traffic is respawning, then you'll have a regular pileup.