Gods in the age of darkness

This seems like it would be a hard question to answer since after the dark ending you can't do anything. What would happen to the gods left in the world when the first flame finally dies? Would they simply be stripped of godhood and become humans? Also what exactly happened to Gwyn and the Witch of Izalith in the first place to make them gods? WOuld their surviving children simply have whatever made their parents gods taken away?

I believe it was the Lord Souls that made them powerful, but you obtain souls as the chosen undead to be able to combat and kill them.

Also Im not sure about you but usually all my Gods are dead before I enter NG+..

Well firstly the gods that you can kill dont incorporate all the gods in the world. Gwynevere and Flann may still be alive out there somewhere just to name 2.

if it was the lord souls that made them powerful it does not make sense for their children to be powerful as gwyndolin's soul is just an ordinary soul, not a lord soul (since you dont need it to access the kiln).

I would not say that it is assured that they would perish. However, I think that it would be much more difficult for them to survive (but then I think that it would be more difficult for humans to survive as well).