Lynn did leave and Éabha is a new permanent member. While Lynn surely might make some guest appearances in the future (and I hope she will) she is not a current member of Celtic Woman anymore.
This hasn't been confirmed yet. The only thing that has been confirmed is that Lynn will remain a member of Celtic Woman until the end of the year and is supposed to be on the next album. This was posted on their website some time ago. I just think Lynn may remain as a member but as a backup in case one of the girls needs a break. They don't need to be permanent to be a member.