There is no \"clearing of accounts,\" but there are wipes, as it so happens in every developing game, that are needed to clear up exploiters, adjust balancing issues, etc. They are not scheduled, but done \"as needed\" - and when needed only. If there is a way to avoid a wipe, the development team will avoid it. Inactive accounts are not removed, unless an individual fails to recreate his or her account after a wipe.
Backups of accounts would only save your character name - nothing else, since both inventory and skills/stats will be removed at some point.