Of course Pokemon would have remained successful, this isn't even a question. It was the best selling game of the year in Japan in 1996 (beating out Final Fantasy 7), and to this day they are the best selling games in Japan period. Even once the rest of the world got them over the next two years, they were flying off the shelves; to date it's the fastest selling game on the Game Boy in the US. It had an absurd marketing campaign as well, such that Pokemon was literally everywhere; clothes, backpacks, lunchboxes, toys, cereals, snack foods, shows, music, anywhere you looked you could probably find Pokemon, and the bulk of the advertising did not utilize Mew. To attribute the series' success to one Pokemon is a gross oversimplification.