Not sure if TG could entirely vacate Suvarnabhumi for political reasons. It would just be too embarassing.
However, there is the other point. The new aiport is quickly reaching capacity. It was opened with a nominal capacity of 45 million pax and existing volume in Don Muang of almost 40 million, but with growth rates of around 10% per year it will soon be stretched. It has a theoretical ultimate capacity of 100 million, but that would require quite a lot of upgrading before it could do that.
I guess it is going to take about a year to fix all the problems at Suvarnabhumi, during which time they will have to close sections of the airport to do it. At the end of that, the expected passenger throughput will be roughly its existing design capacity. Once the problems are fixed, they will have to immediately begin expansion work, which will entail closing sections of the airport to do it...
