How long do DVD's last?

Yes a DVD can wear out. All materals degrade with time and the plastics and other materials used in DVDs are no exception but it will take a (very) long time and the degradation has very little to do with whether or not the DVD is played many times. Recordable DVD's (and even more so Re-recordable DVDs) have a shorter lifespan than the commercial (pressed from a matrix) disks. The greatest risk to the information stored on a DVD is still mechanical abrasion due to handling the disk.