The article in question - http://www.uwgb.edu/dutchs/WestTech/xmongol.htm
I ask because, while it seems to make sense on the surface, I don't know much about the Abbasid Caliphate, nor sociology, nor much of any of the social sciences when related to such an event - furthermore, Dutch is a Natural Scientist, and this is a paper on history, as such, even though he may be correct, I immediately question his authority on the matter.
The claim seems pretty dubious to me. Certainly the fall of the Calpihate shocked the Muslim world but the Abbasid Caliphate had long been in decline. While other rulers might pay lip service to the idea of owing the Caliph allegiance in reality the Caliph only controlled a relatively small area, about the size of Iraq and was often only a puppet of another group. The city of Baghdad itself had similarly declined in importance and the Calpihate's power shrank and there were many other cities that had taken its place as important centres of scholarship e.g. Cairo
while he may be a natural scientist it's a pretty common view of the era and indeed may be viewed as the orthodox view of the event and of the decline of Islam intellectually. I don't know enough to personally evaluate the claim but as a long time listener of the history of philosophy podcast, i know Peter Adamson disagrees. Adamson is a philosopher whose work is in the Islamic world and claims the decline your talking about didn't really happen, rather it's a problem of the sources the west is using. Podcasts 182-195 are partially attempts to rebut this claim to show how philosophy and learning continued on into the Mongol era.
While Adamson isn't a historian his research interests does give his opinions authority.
what evidence does he provide?