With Who Framed Roger Rabbit, it’s not really clear whether the author originally came up with such a great idea and script, or if Disney just brought it to life so brilliantly on screen. I’m leaning toward the second. It’s cool that he got the rights back, but without Disney this idea just isn’t going to "sing" again.
It would be difficult. Aside from the characters and the cast, one of the biggest heroes of the movie was the script. It was dense with irony, jokes about the noir genre, straight man/funny man jokes and physical humor. You don't need the original cast to make a new Chinatown comedy with toons. It's a matter of assembling a story that's interesting and funny, with associated recognizable cartoon characters.