Do porcelain veneers break or come off?

Any form of porcelain veneer can come off. The likelihood of them coming off when they are cemented to the enamel of the teeth (which usually is the case when there is no tooth reduction or drilling) it has a low risk of de-bonding as bond is very strong to enamel. In this cases it is more likely that the veneer breaks due to excessive forces or inappropriate habits and diets. If a veneer breaks off, then almost certainly it needs to be replaced.