Electric boat motors tend to last a very long time because they are mechanically simple. Where a petrol engine has hundreds of moving parts, pistons, valves, oil and a fuel system to wear out, an electric motor is essentially a single rotating shaft. There is no combustion, no oil changes and far less to go wrong, so the motor itself can comfortably outlast the boat with minimal maintenance.
The part that ages is the battery, not the motor. Lithium batteries are rated in charge cycles, often well over a thousand full cycles before capacity drops noticeably. For typical recreational use of a weekend here and an afternoon there, that translates into many years of service before you would think about a replacement.
Saltwater, of course, is hard on any equipment, so rinsing and basic care still matter. But for the propulsion itself, longevity is one of the quiet advantages of going electric.
To understand how to choose a motor in the first place, see electric boat motor power: how many kW do you really need.