Your example specifically contradicts your point.

Judaism is alive and well as a minority group in many many parts of the world. "Dilution" has never threatened the existence of Judaism.

The one thing that did was actual genocide, as a result of racism and xenophobia because of fear that the Jews, the minority group, were destroying German culture. Go figure.

But a few immigrants? I think Judaism, or really any culture, is stronger than that.

Another interesting example is indigenous populations in Canada, Australia, and the US. Those cultures have remained strong with the exception of those where active attempts to extinguish them have occurred. The Canadian residential school system is a disgusting, shameful example of the latter.

Frankly, I'd be very interested to see an example where simple "dilution" has actually led to the destruction of a culture. I can't think of one.

I like that idea, that dilution strengthens rather that weakens. Comes down to what's really important to a culture, and what's incidental. And fear of change. A much healthier attitude than 'resist change at any cost'.