There's no trigger for that. You'd need to use CRON with probably a Query action and triggers set to None. The CRON would target the auto actions URL. You'd then need to put all those checks in a custom SQL to delete those baskets and any other data attached to the basket directly in the database. Probably easier to just filter CBSubs > Baskets once every 6 months to a year and clear them manually. Baskets won't expire if in a Pending state; maybe a feature to consider in a future release (e.g. expire baskets pending for 3 months).