As I understand it currently, if the server config has respawn on:
The asteroid content of the sector is essentially set on sector discovery. As in, first time the asteroids in the sector spawn in, they are "fixed".
If you eat the entire sector, every last block, then after a set amount of time (server config option) the entire sector will revert back to its original condition, aka the asteroids will respawn.
If you only eat parts of the asteroids, leave some there, or miss a few blocks, then the sector will not respawn.
The sector has to be unloaded (aka, no one around to see it) before it will respawn (mechanically, when you move close enough to the sector for it to load, it checks and sees that it was empty last and restores the original asteroid population, if it doesn't get to make that load check, it doesn't have the chance to revert).