Just like the gold standard, a paper money system was created with gold as backing, and as gold backing was made redundant at a point. It's equally plausible to create a paper system with 25 million bitcoins and get rid of Bitcoin backing at some point.
As the "paper system" would not decrease transaction costs, it would not be accepted by market participants as a substitute for native Bitcoin. Acceptance is a prerequisite for both credit expansion, and a removal of backing ("fiatisation" of commodities). This is a critical difference between gold and Bitcoin.