They've never took an official stance on this, but I doubt they ever delete inactive characters on inactive accounts. MMOs used to do this way back when data retention wasn't as trivial and cheap as it is today. I know people that reactivated FF11 accounts that were inactive for 10 years and their characters were still around. I know more than a few people that had not played 1.0 since the first few months it was released come back to ARR with their account and characters fully intact so I don't really think they have a process for deleting old, inactive accounts.