it is conceivable that the ratio will return to roughly where it was two centuries ago, with the Orthodox again constituting the great majority of Jews. Were that to happen, the non-Orthodox phenomenon could seem in retrospect merely an episode, an interesting, eventful, consequential, and yet doomed search for alternatives, suggesting that living by the law may be essential for maintaining a Jewish identity over the long term

Or this (quoted from Hillel Halkin):

Assimilation and cultural renaissance are thus two sides of the same coin of American Jewish life, and all of the wordy arguments about what direction American Jewry is going in are largely a matter of which side of the coin one is looking at. The American Jewish community is rapidly polarizing into more and more assimilated Jews, on the one hand, and more and more Jewish Jews, on the other. The broad ethnic middle has fallen out of it.

Go here to see the entire fascinating article.