Hi Prof.Oak, it's nice to hear from you. It happened just before July 4th I think. The theory in the street is that an imgflip moderator did it, because every comment he ever made was gone at the same time. His memes are still around, but now they say by user "anonymous".
There were a bunch of imposter accounts after 123Guy's account was deleted. I tracked them all for a little while here
imgflip.com/i/1scbuu but lost interest.
123Guy probably came back to imgflip, and he might be one of those accounts I was tracking. Even so, I don't hold a grudge against 123Guy and now just try to have fun on imgflip.