As Giovanni is the archetype character of the Archnemesis and what is known as the Big Bad and maybe even Evil Genius, he is doomed for a harsh and disgraceful downfall. Upon reading TvTropes, I have found that he does indeed fit these categories and TvTropes states for the "Big Bad" that: "The Big Bad may be confronted frequently, but is too powerful to finish off until the last episode of the sequence. The Big Bad may work through Evil Minions..." This is all too true of Giovanni. Through the course of the essays of this site I had stated that in the games, Giovanni is met several times. He is not defeated until the last Gym Match and even though he disppears, in the following games you have to defeat his minions. Even though in the anime Ash never really faces Giovanni, he is constantly dealing with his minions. So what caused his downfall?
There was a fluxuation in power. The hero in the games easily crushed him and forced him to step down from his position, almost the same in the comics. Giovanni, the evil villain, must be destroyed. In the anime, his greatest loss was Mewtwo. Mewtwo was the key to his plans. In the anime he continues to run Team Rocket but it does seem that Team Rocket has significantly lost a lot of their power and Giovanni does not have control over the authorities. Giovanni has lost his powers and has now become that of a comic relief.
Looking back at the games, Giovanni had left Team Rocket to fend for themselves. He had, after being defeated, up and disappeared and no one could find him. His life after Team Rocket was lowly as he hid in a cave for several years with nothing but his Pokemon and a small radio. It had become a life of self pity and looking back and what he used to have: the love and attention of his minions, money, and power. He had put himself in his own prison both mentally and physically. Giovanni, after his downfall, was never to return.
His impressions he made in the world of Pokemon could never be forgotten. He taught the world of his power and authority over the ground-type, his intelligence in studying and training Pokemon. His role and power as being the Eighth and Final Gym Leader of the original games. And in other mediums: his literature and Mewtwo, the original Legendary Pokemon. It can be difficult to see this character aside from his lust of money and power but with someone of his personality and great intellect, it would seem the typical route.