what happened?

[Cli Max imum]

when destiny islands was destroyed to tidus wakka and the other girl? why didnt they end up in travese town? theres this one kid who kinda looks like tidus but he is not

 

[Soldier]

when destiny islands was destroyed to tidus wakka and the other girl? why didnt they end up in travese town? theres this one kid who kinda looks like tidus but he is not

I'll field that question!
Okay, so it goes like this, the fairy godmother explains in the beginning of the game that when a world vanishes, so do it's inhabitants, as they fade into darkness. Some creatures are an exception to this, because they have strong hearts (which are the summon gems in the first game), but for the most part, they're gone. Tidus Selphie and wakka are not present in Traverse Town because only SOME people manage to get there, whether it be by gummi ship or a corridor of darkness.
And in answer to the tidus-lookalike, he's just there to fill in the scenery of the town and hammer home the "this is where people go when they lose their home" fact. In fact, there is also a wakka look-alike that can be seen in Agrabah after defeating Jafar, but only ONCE, after leaving the world he disappears.