If you maintain your pool, copper pipes and heat exchangers will last indefinitely.

The most common reason they don't is low pH + extreme high chlorine from skimmer tabs + long pump-off timer cycles. You can also kill exchangers by calcium build up. The 1st problem results in inside-out failure (and high copper levels in the pool); the 2nd results in outside-in failures, and black copper oxide flaking (plus fin damage) from overheating. Using a salt system can also cause damage to a pure copper xchanger.

Getting a new heater with a cupro-nickel exchanger will allow you to use a salt system, but will not make you immune to damage from low pH or calcium build-up.