Nobody is denying the importance of maintenance, but just keeping plants out and the roof from seeping will get you a long way. The most important effect of the use as a church was that it limited (but far from completely prevented) spoilification, and that (cheaper) replacements were installed when the original gilded bronze roof was taken. Much of what we intuitively assume to be natural decay is the result of mining disused buildings for materials how the damage inflicted by that then accelerates natural decay.