While I’ll readily concede that Japan has surprised everyone, at some point in time the sheer magnitude will overcome the lenders’ belief. Their ability to repay, and then it all goes downhill very fast.
That’s the thing - hyperinflation happens fast. You usually don’t see inflation, high inflation, higher inflation, and then hyperinflation. Instead you see slow deterioration and then a huge jump in a short period of time. It’s like falling off a cliff in its suddenness.