Board Thread:Warhammer 40k General Discussion/@comment-192.138.62.36-20140116164341/@comment-6078851-20140118022557

the bulk of the tyranid race isn't yet inside the galaxy, what we've seen so far is the most minscule atom of the tip of the iceberg - the bulk of the race hasn't even woken up yet (this isn't opinion but codex info) :)

if the imperium collapsed then it doesn't matter how many mini-empires that are left to fill the void - they would all perish. but even the imperium is destined to perish, and it's been doing so, slowly, for 10,000 years, but the arrival of the tyranid race will just speed that up a little.

the eldar are a doomed and dying race already so there's no real need for them to suddenly vanish.

and as for them being ported elves: almost every 40k race is ported - imperium/empire, eldar/elves (+ dark), orks/orcs, gretchin/goblins, ogryns/ogres, ratlings/halflings, dwarfs/dwarfs (although tyranids officially killed 40k's dwarfs). not to mention the chaos gods...