I have a plan in CBSubs with yearly subscription. The subscription can be renewed manually by paying, but should also renew automatically if it has run out, and the user then buys a product on the site.
In an auto action i use the trigger joomla_onAfterPaymentSuccess - this triggers a renewal if [var1_total_amount] != 0 (free products do not give renewal) and if the subscription status is Expired or Unsubscriped.
I do not know if the last condition allready is changeed when the trigger for the auto action fires ? Then it is worthless.