I agree it would be very unlikely the city could back out now. But for me, given the history of the politics of it all and the city's dalliances with large transit proposals in the past, I won't rest easy until the thing is operating.
And this is just about the sweetest sweetheart deal ever. It would take a level of foolishness far beyond that displayed by some of our past mayors and councillors to put a stop to it all. But they've often shown they're very capable of it.
Changing senior governments do alter spending plans too though. The cancellation of funding for the Red Hill Valley Parkway by the Bob Rae NDP government in 1990 is still a sore point for many (bridges for streets crossing the route had already been built or begun, though construction on the roadway itself hadn't started). Now, they didn't say they would do that, but I also don't recall them saying they would not leading up to the election.
The city's next steps are to start planning changes to the connecting bus services (if they have not already) to maximize efficiency of the network and meet the changes in transit demand, continue with complementary land use planning, and get a move on planning and executing services on the other major transit corridors including improvements to the A-Line.