Clincher rims have lips that kinda hooks tire beads, so there is some kind of mechanical attachment. Sew ups are dependent solely on your "glue", and this is where a problem can arise, if the adhesive were to fail. I have never heard of an alloy clincher rim failing on descents. It is definitely possible with full carbon clinchers, however.

Full carbon clinchers are another kettle of fish, because of the brake tracks getting overheated, which can result in "warping" or failures of other kind.