I reckon you need to kill the heralds in order to upgrade the Tier level. Not 100% sure but the 2 heralds spawning next to each others at the same Tier makes me think so. And when having 2 Ires but spawns one after the other the Tier was +1 and not same level.
For your question about not killing, no, I dont try this kind of thing, I think it is silly to do so. Just kill the heralds, and get tour +1 Tier - until T5.
I dont see why they would despawn tho. No mob despawns in the game, but the heralds would ?
Even if you spawn mobs in TZ, dont kill em, TZ changes, the mobs are still under TZ in the first area.
Probably to prevent from despawning.
Will these mobs be able to count for an Ire, even if the area is not under TZ anymore ? I have yet to find this out. Havent had an Ire from TZ mobs in a no-more TZ areza tho
Thanks for the reply. I had a silly idea of clearing TZ areas with a proper S tier build quickly, then coming back with a horker to just snipe herald for double drop. Cheers