The answer for me is yes. I absolutely have. In one particular case, it was heartbreaking but finally proved recoverable; my original Final Fantasy XI account was saved with the help of a very patient customer service representative and a boxed expansion from years ago. So now I can play that account again. (All right, I got all of that back a couple of years ago, we’re using a loose definition of “now.”)
But there is account information I have lost that appears to be gone for good. My original Guild Wars account is gone. I have a box edition of TERA but I’m also pretty sure that the email that’s registered to is no longer even accessible. My first Guild Wars 2 account? Gone. (Also, I think I lost my second Guild Wars account, too, so perhaps I’m just not supposed to be in Tyria.) If you look into the distance, you may find my original WildStar account, because I sure can’t.
All of these games still have a place on my shelf, but it’s more in memorial than anything; what I really bought was the serial numbers for these accounts, and they’re all used up now. So what about you, dear readers? Have you ever lost your MMO account information?