During the period after the new teeth are fitted, the success of each treatment stage will be the main factor determining how the implants are performing.
Once the implants and surrounding soft tissues are seen to be healthy and the new teeth comfortable and correctly adjusted, it is the quality of your home care and willingness to present for regular maintenance reviews that will have most influence on how long they will last.
When poorly cared for, implants will develop a covering of hard and soft deposits (calculus and plaque) which is very similar to that found on neglected natural teeth. Untreated, these deposits can lead to gum infection, bleeding, soreness and general discomfort, just as can occur around natural teeth. It could probably be said that implants much like teeth will last for as long as you can keep them clean.
Well maintained implants placed into adequate bone can be expected to last for many years and probably for your lifetime. However, just as you would expect conventional crowns, bridges and fillings to need occasional repairs or replacements during their lifetime, your implant-supported teeth may also have similar maintenance requirements over theirs.