It is possible, but then again maybe not. If you were ever demoted from guild leader status, they should have sent you an email (although it would have been your email address you provided many years ago and perhaps that would not change). They have recently changed it so that if no active guild leaders log on for a month or so, they send an email out to them all. If none still logs on, then they promote the highest ranked active person in the guild and demote all guild leaders to Level 9.
So, if the person now playing was not originally a GM of the guild with you, then it is possible you no longer have this status. I wouldn't think that would be a big deal in you deciding to come back or not. Being the GM of a one person guild is not really a high powered position you can never regain : )
YOu can always create a new one and start over.