While the collaboration on arcade Taiko no Tatsujin has ended with the month of February, and the collab songs stay in the Game Music folder like any other GM song, that is far from the last we will hear from the idols. Way, way far.
The upcoming Cinderella Girls soundtrack "THE IDOLM@STER CINDERELLA MASTER Treasure☆" (March 22nd, 2017) will include the collaborative remixes of Taiko staple Angel Dream as bonus tracks. In addition to the base version with the ensemble of Riina Tada (多田李衣菜, CV: Ruriko Aoki), Chieri Ogata (緒方智絵里, CV: Naomi Oozora) and Rika Jougasaki (城ヶ崎莉嘉, CV: Kibou Yamamoto), each of the idols also stars in their own solo remix.
About Angel Dream going to Cinderella Girls Starlight Stage, the ensemble version might be the one to be used, but we'll report deeper as the full extent of their collab efforts come out.
Announcement post: Columbia Japan Idolm@ster portal