The lead time for many of the parts is over two years. So it's not just the final assembly hall - it's the entire supply chain, much of which has already been repurposed.
It would cost billions to start it up again, and by Airbus's own admission, the A380 program was only cash flow positive for only a few years (the production rate the rest of the time was too low to be profitable).
Boeing is biting the bullet on the 747 - while it still has a viable freighter market (unlike the A380), the production rate is too low to be profitable. When the fuselage vendor announced they were going to close the facility where the panels were made, Boeing had the choice to make the investment to take the tooling and restart fuselage production elsewhere, but determined that in wasn't a wise use of money and resources.
Face it - A380 production is dead and buried, soon to be followed by the 747-8.