Non-religious Jews will assimilate, intermarry and very often end up religiously adrift. Some will simply cease to practice; others will be agnostic or atheist; some will become Christian. This has always happened, and it happens very rapidly when (as in most of America today) anti-Semitism ceases to be a major factor. The Jewish community is well aware of this; in the various mixed marriages among my friends over the years, the opposition has always come from the Jewish parents, and always because of the fear of assimilation. But in my limited experience, that objection has never, in the end, blocked the marriage.
I believe the IQ tests, and I sometimes think that the mostly liberal Jewish parents of my acquaintance, although they are much too polite to mention it, are counting on selective sorting via academic competence (coupled with residual cultural Judaism) to steer their kids into a nice, safe Jewish marriage. This is not a reliable strategy when Jews are only 1-2 percent of the population. Even in academically selective institutions, Jews will be heavily outnumbered. Without an explicit religious commitment, the rate of intermarriage will be very high.
“(as in most of America today) anti-Semitism ceases to be a major factor”
I see a big rise in anti-Semitism in the US, mostly Muslim-student led on campuses, or lefty-led. The left has become extremely anti-Semitic, interestingly enough as it’s the left these libs identify with more than Judaism. I think it’s becoming a major issue.