The sunk cost fallacy means that you should compare future costs to future costs, not that you should automatically discount all past efforts to a value of zero

The sunk cost fallacy means that you should compare future costs to future costs, not that you should automatically discount all past efforts to a value of zero. You still have to consider the cost of reacquiring institutional knowledge and rebuilding the team and project from scratch. That particular "sunk cost" needs to be considered in the calculation.