If the color of the bag is distinctively different from its surroundings and especially from the person who's jumping on it, it should be relatively easy to remove it from the picture. It would help a lot if the scene could be filmed from the same place before and after the bag has been brought to its place. However it is not an absolute necessity. To get the final hit on ground to look realistic it will probably require another shot of the person jumping on some more rigid platform (from lower height of course ;D) as the bag seems to engulf the person and thus making compositing from very hard to impossible.