A cable doesn't usually give warning. It frays quietly inside the drum groove for months, then lets go the next time the door cycles - often with the door halfway up, which is the point of maximum load. When that happens, the door can drop hard on one side, bend the track, or come off the rollers entirely. We don't recommend patching a single cable on a door this old and calling it done; if one went at 35 years, the other is close behind, and a mismatched pair puts uneven strain on the opener's drive mechanism. One honest limit: we don't do same-day emergency runs to Champlin. We're coming from Edina, 20 miles out, so if a cable snaps and the door's stuck open or shut, get the door manually secured and call to get on the schedule - don't try to force it closed by hand, since a loaded spring with a broken cable is the most common way people hurt a hand or a back on this kind of repair.