When it comes to statutory spending, nothing in particular would happen. These expenditures already are allowed under separate pieces of legislation.
When it comes to voted authorities, it would mean that departments and agencies seeking funding in the supplementary estimates (B) would need to cash-manage and reduce spending in other areas, or postpone some expenditures, or use surpluses from other programs to fund what they are seeking funding for in the supplementary estimates (B), or, in some cases, suspend specific types of operations.
I don't have a clear window as to which departments and agencies will be running out of cash before the end of the fiscal year in the absence of the supplementary estimates (B). This is something that the minister, the President of the Treasury Board, and individual ministers would be in a much better position to explain.