Elseworlds means not within the continuity of the main comic titles. This is not within the continuity of the main comic titles.
Frankly, I'm almost rooting for them to kill off Batman. It would be an incredibly ballsy move, that would be remembered for a long time. Also, if certain speculation is to be believed:
then it plays perfectly to the theme of Batman being more than a man, but an ideal and a legend. It would be a perfect way to end this trilogy.
The next Batman movie is going to be a reboot anyways. No matter what, Batman will be alive and well and played by a different actor with a different crew behind it. It will not follow the continuity established in the Nolan trilogy. So, by all means: Kill Bruce Wayne.