I think the question is a bit tricky, in that sales figures are not going to plummet the way they would in something like movies or music. That is, 15% of US households had a computer in 1990. By 2000, over 50% of households had one. So, it could always be a situation where sales didn't drop, but a new audience came and replaced the previous audience as they had more money to spend. (In the UK, it went from 17% in 1990 to 40% by 2000.)

Second, Europe wasn't hit the same way as the US was. Being from the US, I remember reading that the Adventure Game genre was still alive in Europe in the late 1990s where it was almost completely dead in the USA. You talk Broken Sword, The Last Express or Grim Fandango, those would have been successes in Europe, but not so much in the USA.

That's why, for me at least, Myst was the beginning of the end for the Adventure Game genre here in the USA. It was a huge seller, but when looking at the genre as a whole, 1993 was the last great year for the genre.

Back then, and even to this day, the Monkey Island games are the most well known even to people that never played adventure games.

I've noticed that as well, surprised me more than once!