What about forgotten as in stuff like the Hundred years War and the Napoleonic wars. We acknowledge and learn about them, but we don't cry or lament over them. A better word would probably be relevant. We might look a swastika today and think "A symbol of hatred and facism", people in the future might look at it and think "A symbol of an evil empire from a long time ago", which then turns into "a symbol of something that happened a long time ago and has little relevancy today".
I suppose I can see that. But then again, WWII is still very relevant today (and over the last 70 years) not just on account of the large losses of life, but due to it's political reasons. It's undeniable that WWII can be seen as an example of the dangers of political extremism, and that's something nations and governments still tackle with today.
I don't see it losing that relevance in the public mind for some time, and a symbol that represents such extremism will be popular.
There will still be a few hundred years where students scribble swastikas in their history text books.