Assuming as obvious that Muslims will not give up their religion and suddenly become good liberal Europeans, success by Wilders and similar political movements would certainly be a huge step in the right direction. Success would mean that eventually Muslims would be strongly encouraged or even forced to leave, and Europe would have a renewed sense of cultural identity.
It would then be a short step to the realization that some cultures are simply unable or unwilling to adopt contemporary liberal European values. Europeans would be much closer to the realization that their individualist, libertarian tradition is fundamentally at odds with pretty much the entire rest of the world.
Moreover, success of these parties would embolden anti-immigration sentiment throughout the West, including countries like the United States whose main immigration problem stems from the failed states of Latin America rather than Islam. There is much to be said for the slippery slope argument that once Muslims are successfully targeted as unassimilable, Europeans and other Westerners will realize that other groups, such as African-derived peoples, Latinos, and Asians, have not been successfully integrated either. One can easily see the anti-immigration movement snowballing as Europe develops a renewed sense of cultural identity and confidence.
Thoughtful people in the West will understand that the pose of enlightened liberalism, tolerance, and pro-multiculturalism is simply a Diaspora strategy designed to diminish the power of the traditional peoples in those societies. It reflects the same brand of ethnic hardball that is being played out in Israel, but in a different context where Jews, as a minority, must make alliances with other groups.
When Westerners come to grips with this reality, it will have a transformative effect on our political culture. The opposition of the organized Jewish community to the rise of an anti-Muslim, philo-Semitic right in Europe will be seen as increasingly threadbare intellectually given the reality of what is going on in Israel. And that too will contribute to the ultimate resurgence of European ethnonationalism.