The Columbia disaster undoubtedly slowed down the ISS project extremely, but I am very confident it will be completed anyway, of course only if the shuttle missions are succesful (something I am very sure about).
But how long will the ISS be used? Certainly nobody invests billions of dollars to retire a station in 2015 when it is completed in 2010, on the other hands the oldest modules were launched in 1998 already if I remember it correctly. MIR was used much longer than it was designed for, and despite the problems this worked out somehow.
So, are there realistical plans on when the ISS will be retired again? My opinion is, as long as it is no danger for the crew, keep it up. This thing should stay in orbit permanently. But what are the real plans?