90 Harbour is such a nice building, but seriously hampered by its surroundings (Gardiner to the north, Harbour St offramp to the south). Abandoning a building never does it any favours either. I seriously dig the glossy black cladding on the ground floor, and the art deco-ish front facade and almost wrap-around windows. Although the siting of 90 Harbour and the Harbour Commission building cause serious issues to future redevelopment of the entire parcel, I would fight it if they tried to demolish 90 Harbour.
If anything the parking lot (on Queen's Quay) west of Waterpark Place just south of 90 Harbour would be a better candidate for the terminal. Also, Metrolinx and GO Transit could even move into 90 Harbour and maybe add a respectful addition to the building.