Symptoms
The button "Restore Terminated Susbcription" is absent for the domain subscriptions (even though the subscription status is Terminated/Stopped).
Cause
That is an expected behaviour since BA 6.0.x. The button used to be present in the previous product versions but it did not restore the subscription correctly - the domain has been left in Canceled status and this status caused issues with further domains operations (e.g. renewal).
There is a feature request #PBA-42534 ("Ability to restore cancelled domain after subscription terminated") to implement a way for domain subscription restoring.