Board Thread:Warhammer 40k General Discussion/@comment-14745711-20130906234048/@comment-6078851-20150402141617

the problem with a mass exodus is that there isn't really anywhere to go. as part of the initial human colonisation of the galaxy they discovered that they were almost never the first ones to get somewhere: they either found long established empires or the remains of ancient empires, and almost everywhere they went it seems that orks were there long before. and you may think bids (i assume you meant 'nids) are boring but they are the single biggest threat to 'turning out the lights'.

the only exodus that's feasible is an exodus to another galaxy. i don't know if the imperium has the capability for such a journey but even if they did getting out will be a problem as it seems that tyranids have somewhat surrounded the galaxy.