I don't think that will affect the broader economy. 10 mil per coin is cheap, BTW. But there's our real challenge - people are blinded by dreams of riches, instead of thinking about how we liberate humanity. I digress... I don't think btc's price has any affect on the usability of the dollar or whatever fiat. If they need to make a 10k dollar note so people can buy a carton of eggs, no problem. That's about what it costs in South Korea, using their won - they didn't start at that point. Wheelbarrows of digits on your credit card is no problem at all. Actually, people would love it, since such high inflation would effectively zero out their existing credit card balance.
But supposing you're right, and the USD becomes unusable because of bitcoin storing a lot of value... Then we have an even worse situation. Anyone doing anything will need a loan from a bank that used to be a btc fund. And loans get repaid with interest. So, ... Oh.
New thought. This is evil... But it might be the solution. So the bitcoin economy is rescued by defaults, which literally have to happen, because interest payments are unpayable with deflationary money. Can't take any chances... We'll have to purposely crash the economy. That's doable. The defaults disperse the btc because businesses pay their suppliers. If the rate of deflation is high enough, or janky enough, no bank can profit on btc... People will suffer, though. Not a good solution, but at least not nothing.
The halving cycle could ripple onwards long after it ends.
Hmm. And I think that means the best business a bitcoiner can be in, other than selling btc, is off grid survival gear.
But it doesn't matter. That's all based on the supposition that saving in btc magically ends the USD. That would only be true if the government couldn't borrow USD. They can always borrow USD. Hyperinflation very well could happen, but plenty of countries have carried on under conditions of hyperinflation.
Well. Stream of consciousness. No point in making it look pretty.