Just imagine how Maus would have been with Anja's diaries if Vladek hadn't destroyed them.
In addition, Art asks his father about the letters of his French friend (a frog) from the camps they corresponded after the war. Vladek regretfully mentions he destroyed those too.
Art mentioned he turned down offers to have the comic turned into an animated movie - it's even alluded to in the second volume.
It was originally going to be one volume, but Spiegelman wanted to get it out ahead of the release of An American Tail, a movie also featuring Jewish mice. Spiegelman has publicly accused the directors Steven Spielberg and Don Bluth of plagiarism, though beyond using cats and mice as a metaphor for racism the similarities between the two works end there.