I want to discuss something i think is going to happen. I think anduin is going to leave the alliance and and become a netural figure for both the horde and alliance. This is going to happen at the end of shadowlands.
or the middle
This is what is needed to restore balance to the universe.
Horde heroes die. Alliance heroes go neutral.
Thus is the way of things.
He has an encrypted model alongside The Jailer.
Meaning they likely share an in-game cinematic together. Should be interesting to see what comes from that.
The real question is after sl and we go back to azeroth. Whose staying dead. And how long has it been on azeroth? Days, weeks, months, years, centuries, or more?
Will anduin for example have been replaced for a long time and lose his crown?
Turulyon is gonna act as a regeant for sw but will he go nuts? How about alleria? With azeroth be wiped out by the scourge well we are away? How about au yrel will she sppear well we are gone?
Lots of possibilities.
Depending on how much faith you put in the whispers of the void, Il’gynoth did say “The golden one claims a vacant throne. The crown of light will bring only darkness”.
Which sounds like he’s referring to Turalyon taking the throne.
From my understanding, time passes slowly in the afterlife. So we’ll experience what feels like years being away but it may not have been but months in Azeroth’s time.
The Jailer is going to body snatch Anduin, walk around as him, and become the supreme ruler of the Alliance.
He will be leaving the Alliance when the Night Elves whack him. So yes. Very soon.
I don’t know the answer to your question OP, but I have a feeling it’s going to tie in with the comic where Anduin is on the ship with Velen, but where Velen doesn’t look aged, Anduin has aged greatly. 
If nothing else, it should be an interesting ride.
The dreanei do call velen the ageless. Dreanei live thousands of years typically and i think velen is already like 5k plus i think.
Wasn’t that comic one possible future but a garunteed fate?
honestly I’m not sure, I think so?
I knew he didn’t age fast, but didn’t know he was that old.
thank you for the info 
Naw.
Aduin will just do some kind of “trade places/no, take me instead” shenanigans like bolvar did and pat himself on the back for it.
Everyone will be misty eyed but his legacy will just be another generic self-sacrafice.
Tyrande, Malfurion and Velen haven’t lost their positions.
At first I thought you meant like him swapping factions which would have made no damn sense. This on the other hand seems like a thing that could happen.
Turalyon is the dadd- I mean King we need in the Alliance.
Good bye little boy Anduin. It was nice knowing yah…kinda. Not really though! 
Aye i forget his exact age i know it’s really high though. Certain races like elves and dreanei live really long lives.
Then we have medivhs mom thats using magic to be immortal (as far as aging) and keep her youthful looks.
Well we are in sl azeroth gets swarmed by zombies and has to try and survive.
Velen is over 15K, though we don’t know his exact age. The whole “Eredar joining Sargeras” thing happened roughly 12.5K years ago IIRC.
So did a quick google search velen is apparantly at least 25 thousnad years old… so dreanei can live a stupidly long time and be physically/magically really strong.