If it didn't go ahead, I'm guessing they'd have to re-work the whole of the Dec 2020 timetable changes - because the EMR changes will affect a number of other operators where EMR services cross their path e.g. Thameslink, Cross Country, which in turn could impact where those operators cross the path of others.
Providing the infrastructure work is complete and the rolling stock available to undertake driver training, can't see why it wouldn't occur?