All we know die... Thats good end, I think.
Requiem aeternam dona eis, Domine.

Too much mary sue for that to ever happen unfortunately.

Tyranids and Orks are in a war that lasts for the rest of time. At least that's how I see it.

Whoever comes out of that war will utterly dominate the galaxy, neither side can really break the stalemate on that planet.

The orks and nids get even stronger as they fight and they've currently been fighting non stop for 3-4 years in lore now?

It ends when Galactus gets hungry.

Can't see it ever ending. Things may change, factions may die out and be replaced by others, but on the whole none of them can claim ultimate victory over the remaining species.

Probably, but the important thing is that one must and can enjoy the ride to oblivion.

Nids will destroy everything but the necrons in the long run! ^,^

War in 40k will never end. Too many aliens and humans wanting to stake a claim on the galaxy.

Honestly the Tyranids will probably win. They are the ultimate adapters fully equipped with endless soldiers and bio titans. They control like 4 universes apparently and are the perfect fighting race. They will consume all there will ever be.
BUT there are 4 gods that will only get stronger as more and more die MUAHAAHAHAHAHAHAHA.
PS: Orks are still better WAAAAAAAGH!!!