I don't see the former as acceptable either.
With the outturn costs, HS2's business case is basically worthless, it was not worh the money it has cost.
Indeed, the government's own oversight people concluded that
completing phase 1 only had a BCR of 1.1-1.5, even including all the costs associated with cancellation.
Noone would approve this project on this basis.
If infrastructure is really going to be as expensive as it appears, it is likely to also change the type of projects that are approved.
The "growth focused" HS2 project we got would never pass muster in that environment.
The railway's finances are in pretty bad condition as it is, the burning up of political capital on HS2 is likely to cause more problems in the long run than even the cost overruns.