In practice few individual royal mortuary cults were sustained in full strength indefinitely, since the resources, priestly attention and political motivation to maintain them tended to diminish over succeeding generations and reigns, and Egyptologists find clear evidence that offerings at many mortuary temples declined, were curtailed, or were formally consolidated with the cults of other kings within a few generations of a ruler's death, even while the theological expectation that they continue forever remained the ideal the institution was founded on.
Some royal cults nonetheless persisted remarkably long: certain Old and Middle Kingdom kings received offerings, even if reduced, many centuries after their deaths, and particularly revered rulers could become objects of a kind of extended royal ancestor veneration well beyond what a purely functional endowment would have required, blending into the broader Egyptian tradition of honouring notable dead rulers as quasi divine figures. The institution as a whole ended with the broader decline of pharaonic religion and temple culture in the Greco Roman and then Christian periods of Egyptian history, and what survives today, the mortuary temples themselves, their reliefs and inscriptions, and administrative records of their endowments, is the primary evidence from which modern scholarship reconstructs how the cult actually operated rather than the cult's own continuous unbroken practice.