They aren't going to allow some bitcoin powered mad max civilization to rise from the ashes

They won't need to actively work against it - the collapse of fiat means serious, long-term, possibly permanent collapse of regional and national electric grids. It would be years or decades before anyone had the means to even "open" their "wallet".

In the event of a collapse, food will last until it spoils, gold and silver will take you as far as consent will go, and from there, the only currency that spends is lead.