No, that's not the case. The estimates given for cancelling the scheme do assume such a law would be passed - see
https://www.gov.uk/government/publications/hs2-cancellation-cost-advice for the full details.
Abandonment without remediation (i.e. assuming such a law is passed) is estimated to cost "£33bn to as high as £58bn (2025 prices)". "This scenario delivers sites that are safe, stable, and acceptable to local communities through measures such as tunnel capping slabs, partial completion for stability, high quality landscaping, and long-term maintenance readiness." That doesn't even include the ongoing cost of maintenance on the bridges and viaducts that would be left standing. The alternative scenario, without any new laws being passed, was not estimated.
Anyone who, at this stage, thinks it would be a good use of money to just abandon the project is not grounded in reality. Anyone who thinks, after 3 more years of construction, that it would be a good use of money to abandon it, would be delusional.