That is an interesting hypothesis. But, a) The banks may well be able to sell these bonds, just with a higher yield. b) Maybe there are some clients out there

That is an interesting hypothesis. But, a) The banks may well be able to sell these bonds, just with a higher yield. b) Maybe there are some clients out there with lotsa cash (Buffet, Bezos, Gates) who would love to have Elon owe them tens of billions of dollars at 10% yield. If the whole thing goes tits up, then the bondholders own Twitter, not Elon.