Yes, it does look increasingly likely that Don Muang will re-open, although TG are balking at moving their flights there, as most have at least an opportunity for connecting internationally, which would be a pain in the neck. The locos, on the other hand are keen for it to happen. Of course it has not completely closed and still serves around 20 flights a day, with a small staff, and is still able to handle international traffic.
Many things that need to be fixed (such as adding toilets in the main concourse) can only be done by closing large areas, which is impossible at current utilisation levels. There are a myriad of other things that need to be fixed. It may even be necessary to rebuild certain parts of the structure, simply so they can be econmically maintained. The more Suvarnabhumi is looked into, the more they realise it should simply not have been opened when it was. The best thing would be to close the whole thing for a year and fix everything, but that isn't going to happen.