I have developed a script to check for this and will send an email to notify your member before x days before renewal og trial is ending.
This script uses the campaign monitor api where the messages/emails will be sendt from. You need to have a Campaign Monitor account - its free - ( much better than MailChimp) to run this script.
If anyone is interested please contact me at email@example.com
This AddOn is now in beta phase and will be available in few days.
Please see https://gets.io/plugins/rr/
Please contact me if any questions.