The potential for damage depends on where the leak is located. If the leak is at the junction of the manifold to the head, then the leak should be fixed promptly. Exhaust leaks at the manifold gasket have the potential to damage the flange sealing surface on the aluminum cylinder head. I witnessed this on a car owned by someone I know. He drove around with a very distinct sounding exhaust leak for several months. By the time he got around to replacing the manifold gasket the head had already been damaged and a new gasket made no improvement. If, however, the leak is from the exhaust manifold itself, then driving around with it for a little while might not be too offensive. It would be best to closely evaluate where exactly the leak is coming from and proceed appropriately.
Eric