if they "fail", just remove your jersey (i'm assuming you are male and aren't riding bare chested), or borrow one from a passerby and tie it around your waist.

BTW, i had a pair that i wore for a long time, too long as it turned out. i once caught a glimpse of myself in a full length mirror before heading out one day and saw that the lycra had worn away to such an extent above the chamois in back that my butt crack was showing through.

thought i'd share that...