[Semper Idem]

There'll always be religion and religious groups. The question is, how much power will they have? I suspect the best-case situation is that the churches / synagogues / mosques / whatever will be viewed the same way we view our daffy Uncle Ralph who thinks he's Napoleon - as harmless eccentrics with neither power nor influence. The loss of tax-exempt status and the loss of political influence will cut them off at the knees, and that'll be the end of their relevance to the world.