Howie,
A 270 bullet behind the shoulder is quite lethal, even if the kill isn't instantaneous. I would bet my favorite pair of jeans that he is lying within 50 yards of where you lost the blood trail. On a good lung hit like that, when the heavy bleeding stops they are nearly finished. I have found several deer that way. Even if it is too late for a full mount, you could at least maybe do a European skull mount with the impressive tusks.