Yes, and I've already got the Leaf, Silvia, and R32.
The competition ended on June 24th, right? If you go back into GT ACADEMY 2012 and try to play any of the events now, you'll just get a screen telling you that it's no longer available. In other words, you should delete it. It's just a large hole in your HDD right now if you still have it. But it won't affect anything and you'll still get the prize cars depending on how many gold medals you got there.