see
Pedantic Grognard
You can't buy an unconditional right to something from a party that doesn't have an unconditional right to it. Disney can argue the original publisher has to pay the royalties, but if the royalties aren't actually paid, the conditional publication rights Disney bought go away.They don't need to though - companies simply don't inherit that stuff. Look at the issue of Disney not paying royalties to writers (most notably Alan Dean Foster) who have written for franchises Disney later bought. I believe they eventually accepted a moral responsibility, but legally, Disney was right - the company that owes you money does not exist.