The remapping process enhances and optimises the power of the engine within safe limits, not beyond them. Extra power will also result in fewer gear changes, which may actually reduce overall wear.
Manufacturers build in a tolerance to manage the effect of wear and tear on engine parts, production variations and to ensure their warranty claims during their warranty period (normally 3 years) are kept to a minimum. Most race and rally engines are pushed for every last BHP and are therefore more likely to fail. Whilst normal car / van / lorry engines are limited well before multiple failures become likely, each individual engine is different in how far it can be pushed as a result of a remap. A good remap from a quality tuner like MAX TUNE will never get close the limits of component failure.
You may have seen that the other tuning companies within the market place quote vehicle improvements at higher outputs for similar vehicles. Beware of tuners who claim significantly more, it may be that the engine will be pushed too hard and become unreliable.