IGN briefly spoke with actor Liam Neeson and managed to ask him if we would be seeing Ra's al Ghul in the upcoming Christopher Nolan directed The Dark Knight Returns.
Neeson responded in the negative, but did not rule out that he would return to the character at some point.
Keep in mind, that doesn't mean the character of Ra's al Ghul will not be mentioned, as reportedly his daughter, Talia al Ghul, is set to be in The Dark Knight Rises.
When asked about his favorite super hero, the actor replied with "Superman," stating Batman to be to dark.
Look for Liam Neeson in Clash of the Titans 2 soon, as it films at the same time as The Dark Knight Rises.