Two quick CBSubs "facts":
- Child plans don't "revert" to parents.
- CBSubs supports 2 levels of parent plans (more seems unadequate for UX imho).
But:
- When you upgrade from an *exclusive* plan to an other sibbling plan (with same parent), e.g. in your case from "Sponsor" to "Gold Sponsor", and for any reason "Gold Sponsor" is expiring or cancelled before "Sponsor" would have expired, then Sponsor becomes active again, because "Gold Sponsor" has been "Upgraded from" "Sponsor". So if that upgrade is cancelled/reverted, the previous status of the "subscription upgraded from" is re-instated, and if it was active and its expiry date is not passed, then it is reactivated.