You're right, 25 years is a very long period of time. Even though the government works in 25-year and long-term contexts like that, in the private sector many things can change quickly, and 25 years is a lifetime. So I think what PW will have to do--and again, I can't speak on their behalf--is be very careful about what the off-ramps may or may not be in negotiating the terms of the leases and about any financial penalties that may go with those.
Evidence of meeting #41 for Government Operations and Estimates in the 39th Parliament, 1st Session. (The original version is on Parliament’s site, as are the minutes.) The winning word was secretariat.
A recording is available from Parliament.