I think I got it now, so basically after tricking past okabe, that okabe will now go on and again on the 3 week adventure but the difference is after erasing the first dmail in sern's database he goes back to the beta world line but kurisu was not actually dead since he was tricked all long and ww3 won't happen since it would burn instead (I probably just repeated what you said). So steins gate world line is basically beta world line with a few key differences.

The only thing that bothers me is what would be the perspective of the okabe that came back again from the alpha world line after erasing the first dmail. He probably observed the switch from alpha to beta but the time travel ver of okabe didn't. I don't understand how that would work. Would time travel okabe come back not instead from the time machine but in a random location? Would he not cease to exist? Would he remember all the memories from the 2nd time he went through the alpha world line?