Can a person who is declared a saint be stripped of this status if, for example, it comes to light this person had serious moral and character defects?
Canonization is an exercise of papal infallibility, which assures us that the person who has been enrolled into the Church’s canon of saints (i.e., “canonized”) is indeed in heaven. The life of every candidate proposed for canonization is closely studied so as to ensure that any grave moral defects are brought to light before canonization. The miracles required for canonization are considered God’s assurance that the candidate is in heaven. And, we should keep in mind, even canonized saints are not considered to have been sinless or without faults. See the link below for more information.
The Imperfections of the Saints** by Michelle Arnold