Implications of an end to planar war

[JusticeZero]

Assuming a world with a relatively low level of intervention and power level, and with less focus on Clerics (either not around or they just aren't that important), what are the actual implications of one of the sides of the alignment battles of the standard cosmology winning an unqualified total victory over their opposite? For instance, if Heaven, Elysium, etc are lost, conquered, burned to the ground and salted. Barring adventurers popping back from the planes, or various now dead gods appearing to talk to their worshippers, how would people even know?

[Sagitta]

how would people even know?
The righteous dead no longer move on to their eternal reward. They probably hang around as ghosts or similar.

[Falcon X]

Nope. The planes are about belief. Theory is that the planes only exist because primes believed them into existence. Even if you killed all the Lawful Good gods, more would spring up because there are still primes that are Lawfully Good aligned.

Now, the planars might possibly have to go into hiding. More probably whole new planes would spring into existence that weren't corrupted by the evil hordes.

Indeed, it may have happened before. Why else would all the current planes have multiple layers? Perhaps they conquered another plane, incorporated it into their own, and then a new one sprung into existence to take it's place.

There is much precedence for planes floating towards other planes as the beliefs of the people change.
The easiest examples of this are the cities of the Borderlands. Like Curst in Planescape: Torment. Curst borders Carceri, the prison plane. As the people of Curst became more violent and chaotic, the city literally and physically detatched from the Borderlands and sunk into Carceri. Later, when the people became less extreme, it floated back.
The city that borders Limbo is known to always be moving between Limbo and the Borderlands.

So, if the fiends took over Mount Celestia, Mount Celestia would immediately become evil aligned and float over to the lower planes.
After that happened, a new Plane would have to spring into existence, because there would still be Lawful Good primes who would need such an afterlife, and such gods to rule such an afterlife.

Monte Cook wrote Planescape, and when he worked on 3rd edition, he naturally incorporated Planescape into 3rd edition. If you want to know how the planes work in 3rd, read Planescape.
"On Hallowed Ground" would be the most valuable to read. That and "The Planewalker's Handbook"

[me_maikey]

I think that is a war is won, it is won on the material plane. This would make it mildly aligned to whoever the winning party is (normally the material plane is mildly neutral aligned). This would not mean the end of good or evil, just turns them into (more of a) underdog, scheming and preparing to turn the tide.