Do i need to buy all expansion i missed ?
You only need to buy the Legion expansion. Your account should have been auto upgraded to WOD.
Do i get a lvl 100 by reactivating my account
You get a level 100 character boost when you buy Legion expansion.
What i get if i reactivated my account?
Nothing. ( 100 boost if you buy Legion )
Does it worth playing now ?
I think so, don't know much about how the pvp is this expansion though, since im only playing pve.
So best would be if someone else could answer your question on how the pvp is nowadays.
This post was edited by Tandfen on Oct 15 2016 03:46pm