Will Triton moon ever be invisible in the future? If so, why?

It is not possible that Triton will become invisible after some time. The only time when this would happen is when Triton breaks and explodes. There is a possibility that this will happen as this is slowly becoming nearer to Neptune. If it collides with the planet, it will break apart and it will become one of the rings of Neptune.

Astronomers expect that the rings that this moon would form will be brighter than the other rings around the other planets in the solar system. It is a known fact that not all of the items that can be seen in the solar system now will remain constant. There may be changes that will occur in the future that has not been foreseen by astronomers now.