I take "got off his shot" to mean that Trask was successful when he shot Clark. Sort of the same as "bullseye".
Given that Clark's just been exposed to a major hunk of K, that "fading beat of his heart" means he's done for.
Unless this is a dream fic or HG & his time machine shows up or maybe Martha has taken surgery at night school or maybe Mike the Guardian Angel resurrects Clark or....
c
