Do Minions respawn or do they die?

From a lore standpoint, is there just a vast army of expendable minions in the Nexus or is there only like 300 or so that constantly go out, die, and respawn?

I would imagine the minions just die and respawn like champions since theres already a "Death/Respawn" system in place for the champs. Why wouldn't the same force affecting them affect minions?

On the other hand, it'll be cool (or not cool I guess) if there was a huge country of minions that the League of Legends has complete dictatorship over. Then, when a battle starts, the League immediately starts conscripting thousands of minions, arming them with the simplest of tools of battle. That would mean the Nexus would just be a portal for the army's entry.

I don't know, just a thought.