More worlds are burning. more civilisations are being destroyed. Xenos and chaos forces are moving in on all sides, and killing themselves yet multiplying. And the the Golden Throne has a major flaw which means the Emperor is comign to his death.
Its all in the fluff. I'm sorry but its fairly obvious how it will end.
The Imperium will be destroyed and other intelligent xenos races will be wiped out by the never ending tides of Chaos, Ork and Tyranid forces will eventualy become in small numbers, and the Chaos Gods will fall as they have no purpose. Then the Universe will end... and so will GW's reign