The story goes that Gork and Mork caught Nurgle eating their squigs. On seeing that they proceeded to beat the crap out of Nurgle for it. The outcome of the beating resulted in all Orks being immune to all disease. Taking in mind that no lore mentions Orks being immune to all disease (granted they might be to some, but this is a guess, nothing states that either) they still fall to Nurgles diseases so:
Well they did use to exist. What happened to them lorewise later is beyond me. Though no source outright says they never existed. Even the Lexi still has Khorne Orks in the Freebooters section.
Well, to be fair, absolutely positively nothing would survive a GRB. That is I suppose unless the Daemons didn't resort to some arcane physics up yours at the time. Tyranid's wouldn't be able to do that at least.
I do think that pure lore arguments are retarded though. If Greater daemons are supposedly immune to bolter fire, why can (mass) flashlights put them down (unless they're Great Unclean Ones)? Lore arguments to me are like propaganda hype machines, whereas the TT are more like 'real life events.' Until there's a psychic spell that a Daemon can cast that says: "Disregard all friendly casualties last player turn", then all it is basically fan wankery imo that they can do anything and everything they want whenever. Although their exploits do sound hell cool.
No, it's the Table Top rules that are asinine and pointless, as the table top is designed to be (HA) a balanced game. The fluff is how the universe actually operates, as it represents actual events within the universe as opposed to the tabletop, which is purely just game mechanics. For all intents and purposes they are completely separate organisms.
We will devour the tyranids and the turn them into snacks baking them into drugs and cookies. I think chaos could fare well agiasnt the bugs
