Is this a bug? I am seeing the exact same thing you described on one of my opponents profiles. I have put alot of effort into this game and I am worried about being able to continue it.
Questions about "Member Account Closed"

Accounts have been closed in the past when a member was suspected of spamming. If that occurs the account can be reopened. The solution apparently is not to use "cut and paste" in messages.
Members can close their own account. It is possible someone may prefer to erase their presence rather than leaving it forever on the internet.
Whether members close their account or not, some abandon their ongoing games while others resign them before leaving.
I have a member in my group who suddenly disappeared and and a 'Member Account Closed' message appeared when I went to his profile. The games he had going at the time were still present, however. Then, a few days later, he reappeared, the 'account closed message disappeared, and he started playing again.
What's up? What causes an account to close and then reopen?