I'm pretty sure I remember reading that with Sauron destroyed, the Orcs and Trolls literally became mindless. Without Sauron to control them the Orcs and Trolls lost any ability to organise themselves . It's possible some managed to make their way far east and hide there, but for the most part they were eventually hunted down and killed.
Tolkien toyed with the idea of writing a sequel to LOTR called 'The New Shadow' which would have involved people starting some type of orc cult. However Tolkien only wrote 13 pages before quickly abandoning it.