Great artists build upon the work of those who came before them. This is how it’s been for millennia. Why should Disney be the end of the line?
I doubt you have any problem with people profiting off of Shakespeare, Mozart or fairy tales, so what is different about Mickey Mouse?
How many of Disney's cartoons do you think were based on public domain works?
We progress because we're able to build on what previous generations built.
All this adds up to the fact that established characters are already effectively part of the public domain. A perpetual monopoly on children's culture is both unnatural and unjust.
Disney still benefits from trademark law on their characters along with a generous monopoly on new creations. I would argue that extending this further would reduce the incentive to innovate.
I don't know what the parent poster had in mind, but in my view losing most control by now is absolutely right and proper.