Nobody said that "local churches" (like the seven churches of Asia) wouldn't go "belly up." Good Lord have mercy, think of all those used-to-be Catholic churches in Europe that went Protestant! And some are now being retrofitted as restaurants and condos! Think of a thousand churches in the Middle East that were smashed to bits by the Islamic invasions 1300 years ago a and are no more; think of Hagia Sophia in Constantinople/Istanbul, all of whose used-to-be Christian congegrants are scatterd now for centuries, or absorbed by force into Islam, and their magnificent cathedral was turned into a mosque (and now a museum). Belly up!
The promise from Christ is that the Church as-a-whole (the Church cata holos) will not be led astray.
So the whole is greater than the sum of it's parts?
Ok...