Simple as the titles states, spotted vehicles should be removed from the map as soon as the tank that spotted these vehicles is eliminated.
This is not only necessary because it is more realistic and makes intuitively more sense, but also because the current system can be easily abused. A light tank, Type 93 for example, can just run around the map, try to scout as many people as possible for its teammates and if it gets killed, these markings still remain giving its team quite the advantage.