@weeabootrash In the batman universe reviving someone is literally as easy as throwing them into the Lazarus Pits of Ra's al Ghul, or getting revived as undead monsters by the Black Lantern Rings, or revived by the White Lantern corps, or half a dozen other methods.
Does that make killing all the arkham asylum prisoners a good idea? It might reduce the recidivism rate, but may also cause angry zombies to start rising out of the ground, and I could tell you that if ever there was a run where Batman started murdering people the death toll will end up higher than anything the criminals would have killed, simply because it's a comic book and they have hamhanded morals.
Back on this comic, though. Killing someone who's restrained is STILL murder. It just so happens that murder is the correct solution here, and murder is much less problematic if you can resurrect someone instantly.
BUT IT'S STILL MURDER AND YOU'D NEED TO EXPLAIN IT IF IT'S FOUND OUT. Until someone puts an amendment into the law, to say something like "if you stop someone's heart for medical purposes and then revive them, that isn't murder", it's still going to be murder.
-Having said that, any such case would probably lead to a landmark decision being given to say "no, that literally isn't murder" which would lead to case law updating the definition of murder to exclude this fringe scenario.