The bus has come back a couple of times since then, though. He made a cameo at D23 in 2011, leading the audience in a rousing rendition of the ride's song, "One Little Spark," and got his own prequel comic via Disney/Marvel's Disney Kingdoms.
In Jon Buck's Paradise setting CM is mentioned by the cast of sequel series "Paradise:Veil" and is seen in the story Tall Tales, however his best friend Robert Hallman seemingly vanishes after the 9th "CM and Rob" story.
Many toy-driven franchises that go on for multiple incarnations would often find many characters dropped from later series. The most notable case is G.I. Joe's Zarana: Mostly seen as an attempt to add a second female to Cobra, but she never made a screen appearance since the DiC-produced episodes. While she DID receive an expanded role in the DDP Joe comics, she is the only 1982-94-originated female character to never even get a mention in any of IDW's new Joe comics! Even Cover Girl and Pythona get odd appearances every now and then! She doesn't appear in the Larry Hama-penned IDW continuation of G.I.Joe: A Real American Hero AT ALL!