I love these KH sell-off stories.
As Stan points out, it takes years to save for a Kingdom Hall. Given the current restrictions on how much an individual congregation can hold, and given the continual siphoning off of moneys to unknown overseas destinations (as shown in "Britain" branch and the Australian branch published financial statements) I think there will be extremely few new Kindom Halls built, at least in Western countries, in the future.
Once they are sold, they are gone for good.
For a lot of religions, financial problems in the centre would have much impact on the branches. If all the Islamic universities in Mecca went broke, or the Church of England in U.K., or even the Vatican, most of their respective adherents would continue as before. Their places of worship are generally locally owned, and the clergy class is usually autonomous and locally supported. However, with Watchtower effectively owning the Kingdom Halls and controlling literature and broadcasting, I wonder how the average JW would cope, if the Borg went under.
In the short term, selling less essential KH's may make financial sense, but long term, I think by sellling off Kingdom Halls and taking the money, Watchtower is unwittingly slowly eradicating itself, in a way that is hard to reverse.