I think you miss the point of the 'official forums' section. These are forums paid for, and run/moderated, by the bands themselves or their representatives (webmasters, management, whoever).
Dissection already have an official board on HMAS. So why they need one on UM is beyond me - and I doubt they would be willing to pay for the service when they're already receiving a free forum over on HMAS. If the band are back for the long haul, then their forum would probably be moved out of the 'departed' section and into the 'unofficial' section if there was a call for it - otherwise it would simply be removed.
Dissection already have an official board on HMAS. So why they need one on UM is beyond me - and I doubt they would be willing to pay for the service when they're already receiving a free forum over on HMAS. If the band are back for the long haul, then their forum would probably be moved out of the 'departed' section and into the 'unofficial' section if there was a call for it - otherwise it would simply be removed.