You're assuming that anti-Holocaust people are going to outlast pro-Holocaust people, but based on history this seems like a questionable assumption. E.g. it took less than 50 years for LoTR to go from an anti-war parable inspired by the horrors of WW1, to being an action movie glorifying indiscriminate killing. Similarly, compare the photos of people standing in front of Auschwitz with the photos that come up in GIS of people standing in front of the Colosseum:
https://www.123rf.com/photo_36629433_happy-mother-and-baby-g...
Maybe in a thousand years Westerners will forget about Nazism and the swastika, but it doesn't necessarily follow that they will replace that knowledge with the Buddhist interpretation of the same symbol. Sure, stranger things have happened, it's not impossible, but it seems incredibly unlikely.
It's certainly not going to happen within my lifetime or yours.
You, and your fellow Buddhists, need to realize that Hitler had a far more profound impact on Western civilization (unfortunately) than did the Buddha, and that Westerners who recognize the swastika as a symbol of hate do so because for half the world, and most of a century, it has been a symbol of hate.
Those Westerners are not misinformed, or ignorant, or incorrect in doing so, they're interpreting a symbol in the context with which it was introduced to Western culture. You can tell people that it's a misappropriated symbol of peace, but no one in the West is likely ever going to look at a Nazi swastika and see a manji first, even knowing that, any more than Buddhists likely see a manji and think first about Hitler.