Irene is right to suggest what she did, but that's not your problem. Your code is detecting a collision between the ball and the score. When it detects the collision, it removes the object, which happens to be the score. Also, since the ball starts out in the same position as the score (maybe a poor design choice in itself) and hides it, the collision is ...
You could call the initScoreboard() function to create the new GLabel, like this:
GLabel final = initScoreboard(window);
setLabel(final, "Sorry, you lost!");
setLabel(final, "You win! You cleared all bricks!");
setLocation(final, (WIDTH - ...