Provincial Liberals have taken enough beating for changing their plans in the mid-air, and will not want to do it again unless they absolutely have to.
They won this time only because Hudak made PCs look worse than Liberals; next time, PCs will find a more likeable leader.
Sticking to the Scarborough subway plan will make Liberals look somewhat more credible. The city council would need to reach a large majority on the LRT vs subway issue to convince the province to change the course again; something like 30 vs 15. If it is a close vote, the province will go with the subway.
However, the city might backtrack on its portion of funding for the subway. In that case, the province is more likely to shorten the subway (to STC instead of Sheppard), rather than cancel it altogether.