I was there at the end of last week. Local rumour, for what that's worth is that this is increasingly looking like a longer term if not permanent position. The controllers are said still not to be fully trained over onto the new tower, which was said to be the reason for the closure. It is also rumoured that:
1) The lovely new tower can't provide a view into the overhead, creating operational issues; and
2) To meet safety requirements, it is going to be necessary to retain a controller in the 'old' tower - just in case of comms loss to the new system.
These rumours are entirely unsubstantiated but they are commonly cited. If they are untrue, I'm sure they'll be corrected by the airport's administration.