Over the long history of fighting games, there are few villains that are as memorable as M. Bison, or Vega as he is known in Japan. Fondly called 'Dictator' to avoid any misunderstanding about his name, Bison has been around since Street Fighter II and has served as the major antagonist in most of the Street Fighter games.
However, we can now say with some certainty that Street Fighter V was the dictator's last outing, and he is unlikely to show up in the series again.
This was revealed, interestingly, thanks to a Twitter user called Scotia, who did his best to translate the official "Street Fighter V Climax Arts + Zero to 6." This art book features concept art for Street Fighter V, 6, and Street Fighter Zero. Most importantly, it features developer comments on all the Street Fighter V characters. These comments come from Ryuichi Shigeno, who was part of the combat design team for Street Fighter V, and Takayuki Nakayama, who served as the director of the game.
While they made comments on every single character, the ones made on Bison were the most telling. According to Nakayama, the character design was made with the mind of an aging Bison who was at his strongest and who was also at his end.