toothless and the light fury do leave for the hidden world, but they frequently visit new berk.  i agree with the lesson that there comes a point where even best friends must live their own lives, something I’ve come to experience about a year ago, but i disagree with the notion that it must be final / feature such a large gap of time. 

toothless absolutely visits hiccup !  of course, he will be spending a lot of time in the Hidden World to begin with ; everything is new and exciting, and especially if accepting the romantic relationship between the furies ( which i only do with specific writers / my own interpretation. ) But there will be days, if not weeks, where toothless spends time with his best friend and family in new berk. 

the light fury is hesitant, and the first few times leaves toothless to travel alone. but gradually, she begins following him, always sticking close to either fellow fury or other dragons, never caught too close to a human. for her, this is where character development begins to bloom. this wild, untamed creature explores a world she has never known ; much like toothless does the same. 

          creature  of  a  world  long  hidden,  defenses  she  had  built  high  in  face  of  human  come  near  in  territory  unknown.   what  fateful  day,  caught  in  a  tale  of  shackles  and  friendship  alike,  beyond  control  of  star — lit  child.   Had  it  been  different ?   If  wrathful  shot  had  met  its  mark ?   nature’s  giant  reduced  to  mere  splinters,  justified  is  fearful  echo  in  voices  who  speak  of  lightning’s  offspring.  (  o’  beloved  kin,  what  strange  allies  you  bring  before  me  ;  have  you  lost  all  senses ?  )  

          boy  with  dragon’s  soul  /  chieftain  of  another  heart,  how  kind  you  are  to  all  who  would  listen  to  your  words  of  compassion  (  and  even  those  who  do  not  ).   selfless  until  the  very  end  /  until  enemy  knocks  down  heavy  gates  and  marches  for  all  you  love.  how ?   child  of  man,  your  heart  bleeds  emotions,  she  knows  /  feels  it  in  thick  air.

        you  saved  me,  the  boy  says,  and  winged  beast  wishes  she  could  reflect  moments  so  crucial.   but  a  mind  scarred  by  cold  metal  and  searing  poison  dares  not  think  back  on  a  boy  falling,  sacrificing  himself  for  his  best  friend  /  on  cutting  through  harsh  winds  hoping  (  praying  )  the  norns  would  allow  her  to  save  a  life  —  just  this  once.