Whilst it's definately true game sales will suffer as a result , if that's offset by the reduction in costs of not having to produce an Anime then they'll go for it.
Let's not get foolish here. It's true that most people ages 13 -22 already know about the games but do they make up a majority of the sales? I don't think so. The only reason the games are still continuing to this day is because of the animé is still airing and is getting kids around the world interested in the games.
It's may be possible for the Pokémon Company to actually get some profit by ceasing their production of the animé but no one will actually consider it a possibility. This is especially true considering that the animé is cheaply produced to begin with and that it brings in a lot of money as well.