Multiple time lines
Who's to say that there are only 2 timelines. Maybe there are many timelines. I'm wondering if these people are really dead. Isabella says that her and richard are already together. Maybe in another time line? Maybe everyone Hugo sees is dead but alive from another time line. There are connections between these time lines. Kate already started to remember Jack in the ALT but didn't know why. Maybe they all connect or coverge. Wasn't it Jacob who said it only ends once. And Locke said All roads lead here.