What happens when graphics & visuals are needed for special events?

[Shirai]

I know that I wouldn't want to see the company just recycle the same visuals over and over again. Eventually seeing the same visuals over and over again will become boring.

To be blunt, this what will likely happen.
As long as the game is up and maintained there will be things like seasonal events, but they will most likely be repeats of existing content.

To set your mind at ease a little, there should be more than a decade worth of different seasonal events content because they didn't do the same thing every time and most of it should still be in the game.