Trion Worlds has sent out an email as well as posted on the official Rift forums, that players with inactive characters will have their names cleared to make room for incoming players as server merges commence.
If one of your characters is going to be impacted by this change, you'll be getting an email from us in the next day or two with instructions. If you are one of these inactive characters and want to keep your name, you'll just need to log in with that character before October 23rd.
I also want to let you guys know that everyone who is transferring off a shard that is part of next week's unification will be receiving a title denoting where they previously hailed from.
Read the full notice on the Rift site.