I understand this sentence as,'if you kill him, you are following him to the netherworld'.
I intuitively understand this が as conditional but I am not sure. I haven't found anything which ascertains or confirms this. But I have a strong feeling of it being a conditional. What kind of が is this and what is it called ? Also, is this some kind of polite form of たら・なら・ば ?
I've tried searching for this but I think I am missing its name or I am not searching it right. Any links relating to this would be awesome.