Time difference

Hello, i was thinking, when julliet banged the bomb and blew up the island…(i’m guessing thats what created the alter, line). the plane made it back safely. Well… with Sayid killing the dude that shot alex in the head, does that mean alex is alive somewhere? And also can and will the two different realitys affect each other being 3 years apart?, jack and daivd, locke and peggy-in 2004. jack getting beat down by sawyer- 2007…..