Probably Sega would still be making consoles, Nintendo would have been even stronger in the market and Microsoft probably would still enter the console market. Even though Nintendo was always dominating over Sega during their console wars and Sega´s marketing/console add-ons failures, Sony and its PS2 was Sega´s biggest/last nail in its coffin (hardware wise).
Edit: Forgot to mention Sega´s failures.







