The job goes sideways when the cable failure is a symptom, not the cause - usually a spring that's already weak and about to go, or a drum that's worn oval from years of a cable riding wrong. Replace the cable alone on a door like that and you're back out in a few months for the spring. On a house from the early 1960s, we'll also check whether the track and rollers have been replaced since - if not, decades of wear on original rollers can keep a door from tracking true even after a correct cable job.
One honest limit: if the drums are a discontinued size no longer stocked, we may need to order parts rather than finish same visit, and we'll tell you that up front rather than making you wait at the door.