So who is ultimately responsible for lifting the ban?
The airspaces were closed by the ATCOs, so they are the ones to open them. It was an easier decision to close them than the much harder decision to open them. With due respect to the ATCOs, they surely do not have the competencies or authority to lift the ban? Are they experts in weather, engine wear, vulcanism and the myriad of related technical fields of expertise? Having said that, I cannot suggest who is competent to make these decisions.
With severe weather, for example, I understand the ATCOs can advise the flight crew but the ultimate safety decision rests with the commander of the flight, not ATCO. Is this event not similar to abnormal weather, in legal terms?
It will be a very brave administrator who decrees the airpsaces open; they will tend to be ultra-cautious, for obvious reasons.