There are different types of exterminatus. 1. Atmospheric saturation that completely destroy a planet's atmosphere. 2. Life eater virus that kills all flora and fauna. The virus also turns the corpses into a slimey goop that can be easily ignited that burns everything and everyone in the planet's crust. 3. Cyclonic torpedo that completely destroy the planet's core and creating a huge explosion that destroys the planet and kills all its inhabitants. The first two types of exterminatus if done in a planet can easily be repopulated. The third is kinda complicated as the planet is gone and only its rubbles remain.
16:12 The scary thing is. That horse has more in common with a fucking bear then equestrian species. Its genetically altered to be toughened bones and flesh, its muscle tensions are leagues stronger and tougher. And its hooves are replaced with metalic claws that can shread humans. Naturally occouring clawed hooves I may add. These things are also drug addicts, well thats a stretch. Chemicals are constantly pumped into these things, to keep them laser focused, brutally slaughtering any once their rider is gone. And if it goes without these chemicals, it goes berserk. And may self implode. The hearts literally convulsing and blowing up inside, killing the beast. These things are very terrifying if you arent a kriegsman. They are made to be loyal and resililiant.. but only loyal to the krieg as they are only familiar with their handlers, and the uniforms and commands of the krieg.
The Death Korps is honestly my second favorite Imperial Guard Regiment group. It was explained to me that an average of about a hundred worlds are in open revolt across the entire Empire. However since there are millions of worlds in each Segmentum, Command has to prioritize conflicts. Chaos and then Xenoes, take top priority.
I'll try to your question about rules and editions: for most editions of the game an army will get a codex book that contains all the rules for their abilities, sub-factions, units, etc (barring any other expansions, supplements or updates). Through these books new stuff is introduced and no longer supported things (like out of production models) are phased out into Legends (a source of rules for old models that can still be played but not in competitive formats and have limited support). For most of their life Krieg models were produced by Forgeworld (a GW subsidiary that makes specialist, usually niche, models) which have been more likely to be discontinued due to their niche specialist nature (such a thing happened with the Elysian Drop Troops regiment). Luckily, with the new edition of Kill Team we have new GW plastic models for Death Korps of Krieg, so it is unlikely that support for the regiment will be dropped any time soon.
Krieg is fully defended with orbital cannons and fleet destroying graviton world ender artilleries. Sending space marines to be slaughtered without any strategic value is kinda unappealing to the imperium. So they'd rather starve krieg out of resources instead of fighting a costly seige.
