your players will probably just work out that they aren't going to die at all and start taking stupid risks that they shouldn't
you can't just not metagame
if you know a choice will result in a certain outcome, you can no longer make that decision neutrally
in fact, you literally can't take a risk when you know what the outcome of a choice is, because there's no risk to take
not even bothering to roll is barely a step removed from just telling your players "i'm not going to make the enemy roll to hit you because then you might die and you haven't found your long lost brother yet", and if you can't see that that's a garbage scenario for roleplaying i don't know what to tell you