The question would be, what is the effect of an impact on a ribbon, and it's detachment from it's anchors, going to do for any load going up or down that ribbon? My feeling is that it's not particularly healthy to be riding that ribbon, unless your elevator car is actually able to transfer to another ribbon even after it's anchors have detached. Might be a good idea to not be under any likely fall paths from a given spot on a strand either.
From the perspective of over-engineering the project, I would suspect that what you would want to do is have elevators using some combination of 3 or more ribbons, oriented in different directions, with the ability of the load to be handled on any single strand, but with the expectation that at any given time the loss of no more than one strand would be acceptable, and passengers would be expected to evacuate (with appropriate suits and chutes) and cargo loads would be "aimed" at uninhabited areas. (Agreed that may be "interesting" at certain altitudes....)