There is a Lord Shen Petition to bring him back.
I found it and here is the site:
Riolu in Equestria 73Riolu gets ready to attack Belicista; however, if he does this he will have to return to Equestria. He won’t see his human friends again if this happens.Riolu in Equestria 73 by gundamfan2
Back at Equestria, Winery and her witches begin their killing spree. They murdered 25 fillies. Twilight and the others must stop them. Zorua and the other Pokémon need Riolu. Zorua and the other Pokémon have to find the killers without Riolu’s help again.
Zorua misses him.
Meanwhile, Riolu tries to explain to Maud Pie about the upcoming war; however, Maud Pie was uninterested. Riolu tricks her by telling her that inside the battleship, they have some rare rocks.
Maud Pie decides to help him.
Riolu has to find some rocks before Maud Pie finds out the truth.
Later at Equestria, Zorua and the others found a few dead fillies until they found a filly being attacked by Winery and her witches. Zorua and the Pokémon saved the filly. They fight off the evil killers.
Twilight and her friends use the Elements of Harmon
Ash the Riolu: and PikachuAsh the Riolu wakes up to discover he’s in the Pokémon Center. He looks around until he sees the female, yellow Riolu. The female Riolu approaches him and speaks to him in a human language. Ash is shocked that he is able to understand the Pokémon. He realizes that when he became a Pokémon himself, he could now understand other Pokémon.Ash the Riolu: and Pikachu by gundamfan2
Brock and Misty enter the room and they get a chance to look at the cute Pokémon.
Ash tries to communicate with his friends, however, they can’t understand him. When Pikachu comes in, Ash talks to him and sees that he can understand him too.
Ash tells Pikachu who he really is. Ash even tells him a secret that only he and Pikachu know. After hearing the secret, Pikachu is convinced and a little shocked. The yellow female Riolu gives Ash some food which he eats until she kisses him.
Meanwhile, Dr. Kichigai calls someone and he tells him to look for a Riolu. The person is police officer Hadu.