Endings
There are 3 different Endings in Quantum Nucleus.
#1 -> Don't collect all 7 Artifacts. (No chance for special requirement / OR special requirement doesn't do anything)
#2 -> Collect all 7 Artifacts but neglect to fulfill special requirement.
#3 -> Collect all 7 Artifacts and fulfill special requirement. In this case the game is longer.
<insert special requirement here>
Ending #1:
Nova and Asuka don't find or choose not to collect all 7 artifacts.
This prevents FORIS and Khaos from starting up the Lance of Longinus.
So the earth was saved by this fact.
However Nova is ultimately to weak to destroy Khaos and all of FORIS, so they escaped.
Havoc returns to the Creator.
Ending #2:
Nova and Asuka collect all of the 7 artifacts.
Khaos defeats Nova, FORIS starts up the Lance of Longinus and destroy the earth.
The Creator hard-resets the simulation.
Ending #3 (true ending):
Nova and Asuka collect all of the 7 artifacts.
Khaos defeats Nova, FORIS starts up the Lance of Longinus and destroy the earth.
Havoc calls out to the Creator. Nova, Asuka and Havoc are transported to the Creator.
After the Creator exposes the real nature of their multi-verse, in a dialogue of him and Havoc, Nova and Asuka beg the Creator to do a 'rollback'.
Eventually the Creator accepts, under the condition that Nova and Asuka would train in his location, until they are strong enough to stop the lance and FORIS.
If they wouldn't be able to finish FORIS off, the Creator would hard-reset the simulation.