Of course they did. That's why WoW is populated again.
In Hellfire I see maxed out player numbers every night. On both sides and that for 8 year old content and just 2 years ago the world PvP over the Towers never happened, now it changes back and forth every few minutes.
People group up for these objectives all the time and the vast majority are proper lvls for these re-populated zones.
Perhaps some should play these days instead of theorising on hear say.
Also my server got connected on June 24 z2004 ... and ever since our economy went high as a rocket through connected Realm play.
You see the WoW haters, like this reknown one, are pissing their pants ...
for the future now
As connected realms are MUCH better than old server merges as Blizzard can simply add more connections without any actions from players needed.
As for players returning: they will come and will stand in awe of this NEW cross realm play - both in economy and open world zone play introduced over the last year (Sep 2013 till now).
If I were a WoW hater I would be in pure panic mode if you watched the new activity.
Just 2 years ago ALL trolls yelled, the world is empty, these days the slogan is: my world is too populated. And frankly when 2 years ago you could hardly find another dude in Helfire, these days that 8 year old zone is populated as if it were launched 3 weeks ago.
Of course I knew this seamless cross server technology was a breakthrough in design and I say one thing: you ain't even seen nothin' yet, as WoD will even add MORE seamless cross technology.