I noticed that B.D. was missing his helmet in the last frame before I noticed that he was missing his leg. The missing helmet makes a stronger statement about what it means to B.D.
B.D. has always been wearing a helmet of some sort, since he appeared in the first comic strip almost 30 years ago. It's been the symbol of who B.D. is. And now it's gone.
This isn't a cheap emotional ploy on Trudeau's part. It's a very expensive emotional ploy. and it wouldn't be nearly so touching without the decades of history leading up to B.D.'s loss today.