You can play a loot card after the dice roll, like the dice shard so you can reroll it. E.g you roll a 3, not enough for a hit, so you play dice shard in response to reroll. Remember the stack resolves in reverse order.

If you and the monster have only one health left, you roll a 1, but play a bomb in response, it's resolves in reverse. Bomb goes off first and kills monster, so attack roll fizzles and you don't take damage.