I'd be fine with them doing what some other websites I've used do with usernames: if someone doesn't log in for a year, they send that person an e-mail notifying them that because they haven't logged in for a year, their username is now classed as "inactive" and will be deleted in 30 days unless they log in.

That would give people who are still interested in playing the game the chance to keep their names and weed out the ones that really and truly are abandoned. Because, let's be real here, if you haven't logged in in a year or more and you don't respond to an e-mail, you're no longer actively playing. Why shouldn't an active player be able to use the name?