Well, we have historical proof that nearly all companies do pay with real money in the total absence of such government mandates. We definitely don't have proof of the proposition you claim, which is immediately falsified by the most cursory examination of history.
Note also that scrip is denominated in currency and accepted at par. The problem was generally not that you had a lot of scrip and couldn't spend it; the problem was that the company store charged high prices. But the store charged the same prices whether you were spending company scrip or currency.