The Suez Canal was completed in 1869, after ten years of construction. It is still in use now. There is basically no reason why it should not stay in use for another couple of thousand years, assuming that humanity somehow avoids to wipe itself out in the mean time.
In the same way, it would be nice if large scale grid infrastructure (especially submarine power cable connections between Japan and Korea, China, and Russia) could also have a service life of several centuries.
This question has been asked before, and here is one answer, looking at previous experiences.
The weak point of the submarine cable is the insulation, which might age and degrade over time. However, experience with existing infrastructure shows that one can expect at least 40 years of service life, and it might very well be possible to get much more. They explain that the technology for submarine power lines is already very old and there are many projects in use for more than seventy years. They also mention that the world’s first high voltage direct current submarine cable (connecting Sweden and Gotland in 1953) is still in operation.
If modern technology is able to come up with a submarine power cable that lasts for a couple of centuries, that would have obvious advantages for the economics of building that infrastructure.
On the other hand, it would by exactly the same measure not be in the interest of the maker of that cable. If their product lasts forever, they won’t get to build a replacement, and will therefore go out of business once the last connections are established. That might lead to losing the experience and technology, so maybe it is even better to have only around 50 years of useful life.