As far as I know, he heads back to a planet in Alterra controlled space, and that's it.

There's no other information said anywhere (Except one or two data boxes in BZ) and any speculation should be made clear so that people don't misinterpretation the facts.

In the data bank for the cuddle fish it states how similar they are (to intelligance) to dolphins back at earth. And states they've gone extinct. And for the radiation suit the data bank talks about how it was needed for Earth when nucuelar war broke out. Thus why governments fled the planet.

Or... Idk, they didn't flee the planet?

You are making pretty extreme assumptions. I mean, there are places on earth now that are affected by Nuclear radiation where you need a suit, and there are species on earth now that are going extinct, yet we have no real need to leave the entire planet, nor is there any proof that it was destroyed.

I don't see the point in these massive assumptions that we as a species are able to blow up a planet in the near future.

earth is in subnautica why would a caracter in the trailer say that they missed sunlight

The earth can not exist and the sun can still exist

than it would be a different name tho

Or they call the sunlight on 4546B sunlight? That also makes sense?

no they don't

go watch the trailers yourself

In the trailer, they call the sunlight on 4546b sunlight, just like I said.

I fail to see the confusion, it seems pretty obvious.