The story hasn't ended yet, and we still have Chaos Origin Physique, I can guarantee you Nikki is gonna find a way to make us fight her and win despite her being a god, she's literally the main villain ffs
The story will end once MC reaches NS and is forced to leave the poma world. At that strength he's not even strong enough to survive LB giving him a mean look, much less an actual God that is worlds above her.
And Shen Long Mu isn't the main villain, she's a doomsday event that is coming towards the poma world.