This is exactly the fallacy this article is challenging. It is simply not true in business reality, whatever the chalkboard fungibilities.
The difference between a positive and negative float is a structural difference that has long reaching implications. On that chalkboard, the difference between a publicly listed company and a family owned business is trivial or esoteric.. best explained by portfolio theory or somesuch. Sometimes abstractions miss the point.
There is no such thing as "cash is guaranteed to come in at a future date". Counterparty risk is pretty much impossible to remove, only to trade away to another party.
So long as you're running a profitable business, cash flow management does seem to be a pretty trivial problem. The difference between positive and negative float is just a loan. And, if you can show a bank that cash is guaranteed to come in at a future date, you will have no problem bridging the gap with a loan or line of credit.