Because i completed the different zones campaign quests, to the part where u get the popup with “campaign done / world quests and adventuring mode available” - on a character i dont want to play on. I can see on this character that the campaign continues abit more despite the popup with “campaign done”.
TLDR : Do i need to re-complete everything on my new shaman or ?
If you have completed the campaign you can choose what you want to do on alts. I skip the Dalaran intro by talking to Thrall, then I go straight to Dornogal via that skip.
At this point you can do whatever you want, there is a system (it will show you where) to choose a zone you want to level in. You can do that individual zone campaign again if you want or you can just ignore it and do side quests, or you can spam dungeons, delves etc. Whatever you fancy, mix and match as you please.
There may be the odd occasion that the campaign is needed to unlock an place for the right NPCs.