I don't think it really should be a concern. Heath Ledger's death (and to a lesser degree the Joker) obviously brought more more attention to TDK than what was originally expected. However, the movie really delivered and connected with audiences causing the movie to rake in over a billion dollars. My point I am trying to get to is that TDK was HOT when it came out and that will almost secure a very nice opening weekend gross for TDKR, regardless of what the quality of the film will be. Granted, anything is possible, but if you look at other recent blockbuster franchises (Spider-Man, X-Men, Pirates, etc), every time an entry in the series is popular and critically well regarded, the following one always makes out big.