I mentioned this in another thread recently, but the portions of concourse ceiling and train shed ceiling that sit under the Canal Street viaduct are the responsibility of the City of Chicago for maintenance/repair. Amtrak claims that the city has failed to keep the viaduct in a state of good repair. In May, 2015, Amtrak sued the city for damages, claiming Amtrak and Union Station have spent $500,000 in repairs of spalled concrete that are the city's responsibility.
http://cookcountyrecord.com/stories/510579805-amtrak-sues-city-over-condition-of-canal-street-viaduct-at-union-station-alleges-neglected-maintenance
From the pictures in the Sun-Times article, it does not appear that the concrete that fell today was from that area of the train shed, but Amtrak has clearly been aware of the deterioration of the train shed ceiling for a while, and has spent money it probably couldn't afford to make repairs. Steinberg mentions the black netting in the south train shed and I believe that portion is part of the Canal St. viaduct.
Deutsche Bank owns the 222 Riverside building. The 10 and 120 Riverside buildings, which are also built over the north tracks, are owned by Ivanhoe Cambridge, one of the largest real estate companies on the planet. Both companies certainly have deep enough pockets to start repairs almost immediately. Then again, they also have enough lawyers to drag the process out needlessly, if they choose.