Actually, since there have been sveral irrepairable faults found in the Golden Throne in the past while, eventually the Throne will just give out, the Emperor will truly die, and the Warp will be inaccessable for travel. This will result in every Space Marine/Imperial Guard being stranded and the Enemies of the Imperium will annihilate each planet one by one as the Imperial Forces won't be able to reach each other. The other races aren't restricted to the Golden Throne to follow the Warp (from what I can tell) and can take us out at their lesure. This is really

annoying though, the Imperium, specificall the Blood Angels are my fav armies (for now, I'm easily swayed), and although I know this will never actuallly happen in game-terms, as it would result in the end of
40K and/or
GW, I hate knowing that bad things will inevitably happen.