Nice qualifier to exempt those 7 CATHOLIC churches in Asia that went belly up.
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.