In my novel, an ersatz antagonist comes up suddenly (his attack is a surprise, so no way of knowing about him or mentioning him before that). My protagonist arrives and doesn't even meet him, as that antagonist dies during the battle's rout. How do I make it more interesting? I had a thought: this antagonist has a brother, and I thought maybe switching POV's with this brother for that battle could be interesting. So instead of a boring battle for the protagonist's army, you could have the last moments of the brother's death. But the problem still stands, how do I make these deaths matter to the reader? I'm not under any illusion I can force them to feel something, but here they can't feel anything even if they want to.
Does the story switch POV's throughout? If so, you could do the antagonist's POV until he dies then in the next chapter switch views for the aftermath. If the whole story is written from the protagonist's POV it could be confusing to have a sudden switch. You may just have to accept to sticking with the one view, but you could change the battle so the two people are closer together during the fight.
Then yes, it would be within continuity to use the antagonist POV in my opinion. Using A Song of Ice and Fire as reference, the character of Cersei Lannister is used well in this way [better than the show imho]. You see WHY she is doing what she does, even if I don't agree with her motivation. I love it when novels do this, show you that the antagonist is a person and from their viewpoint, why they do what they do. It makes me interested in what happens to them. Not necessarily because I like them as a person or want to see them live or die, but because they are a human, albiet a misguided one sometimes. Or maybe completely justified. History is written by the winners, or so they say. And everyone wants to see themselves as a winner.
