What happened to the Orks, Orahki, Trolls, The Nine?

I know! They all went off & formed "boy" bands!

The books deal with this issue somewhat more "comprehensively". (Sorry; couldn't resist it.)
But the answers do lie within the plot points made in the films. No females and an artificially created race equals no reproduction. Saruman had a little "thing" of his own going in the Shire as I remember it. But he got cleaned up when the boys came home. And the rest of the nasties were supposed to be living on the evil given off by Sauron, so when he croaked, they just withered up and died. The implication was that without the head bad guy to nourish their black little hearts, all the orks were headed the same way.
As good as the movies were, they did drift away from the plot of the books in a number of places. But the skill shown in the screenplays and direction got most of the fans of the books to overlook those "flaws" because the "new" story was so good.

Whowasthatmaskedman did a pretty good job answering. I would add that the orks/ orahki were tracked down by the remaining armies of good men (the Rohirrim, the Godorrians) and slaughtered. If you don't want to read the whole trilogy, read the appendices, it picks up on the before and after of the story and fills in the gaps.