I've always wanted to try above, with those that save versus i.e. fireball live, those that fail die. In other words the save determines the "hit" or not....
But, normally, when I use minions, I just use regular 4e minion rules but in 5e. Basically the monster is the same (so a threat) but has 1hp so dies fast (though never on a miss effect).
I've also used swarm/mob mechanics as some above have suggested - but that doesn't seem as fitting as the regular minion mechanic for your scenario.

