if it don't fall over dead on your first shot keep shooting until it does. all shots should be aimed behind the front shoulder to get the lungs or heart. however, if your shooting cleanup take any opportunity that presents itself.

my brother shot a cow elk earlier this year, double lung passthrough. the elk jumped initially but didn't run off for a couple seconds ...long enough for my brother to knock another arrow. by the time the elk started staggering off he put a second shot in the back of it's head as it was running through the brush...just in case.