Given the context and perceived connotation, "relapse" could work. It may perhaps anthropomorphise the movement too much given it's use in present vernacular. It does sound a lot like recidivism to me though. When a movement or society rests on its laurels of progress, ontologically, but more importantly pathologically the behaviors we once knew in the collective consciousness certainly do return.
Thinking about it more, the comparison to a sober person relapsing on any pathological behavior pattern (after starting the sober life, facing the realities of life with escaping by old behaviors, and learning that it gets better if they continue doing what it took and takes to stay sober), does seem appropriate with respect to the collective conscience of our species. For if the habit, or behavior be truly innate in society (as is implied by returning to the origin), then no period of sobriety cures society of its pathology. When we stop doing the things that overcame society's inertia and sustained progress, the pathology is still there ready to pick up right where it left off. We don't lose the progress we made, but in a sense we have to try again, and seriously consider at what point did we actually start the return. Usually it is not obvious and unfortunately it often starts subtly in the sub-conscious or collective *un*conscious - a place where only dedicated practitioners have awareness - a place where pathology thrives. The limbic system of society.
Anywhere close to where you were wanting to see this go? Perhaps having a family therapist for a parent put me in agreement with Carl Jung. He often thought about these things and the mystery of life for both individuals and the collective.