If a romantic partner sacrifices themselves to in turn trap one of the antagonists (Dont ask how it would take too long to explain, Carissa is a potato) would you have it work? Or would you have the antagonist return making the sacrifice worthless?
I think it depends on what you want to convey to the readers. What kind of emotional "journey" do you want them to go through? I think having love interest's sacrifice work would mean ending the story soon after (or have the endgame with protagonist winning in the end be triggered because of the sacrifice). But if you have antagonist come back, then protagonist can be motivated to defeat antagonist even MORE so that love interest didn't die in vain.