When mouse-hovering over a user name of a closed account, the quick info window pop-up still shows info. When clicking on such account, it just says "This account is closed.". I guess the quick info pop-up window should be consistent with that, and just state "This account is closed."
For an example, see the Fenris1066 user at http://en.lichess.org/forum/lichess-feedback/goodbye-lichess
For an example, see the Fenris1066 user at http://en.lichess.org/forum/lichess-feedback/goodbye-lichess