This isn't true. Sheppard being mothballed was used as an example of what might need to happen if city council didn't approve the land transfer tax and vehicle registration fee. It was just used as an example of a potential cut.
If you say so...
Remember that surface routes 'lose' far more money than Sheppard, but making peripheral cuts to them doesn't jab Mel Lastman, doesn't jab subways, doesn't jab the North York/suburban planning model. You can't cut Sheppard without spending millions adding the bus service back, which is impossible since it would need to be probably more than twice as busy as Finch East. Millions more would be lost when some of the ridership is killed. Mothballing Sheppard would save no money.
The DRL has the potential to replace an enormous quantity of surface routes and vehicles if it's built long enough and with enough stations on certain alignments, but it's too soon to say if that efficiency feature will be touted as a reason for governments to back the project.