Central banks will just buy them onto their balance sheets. Its already begun:
https://ftalphaville.ft.com/2020/04/30/1588254981000/How-sho...
https://www.afr.com/markets/debt-markets/why-the-rba-is-lend...
https://ftalphaville.ft.com/2020/04/30/1588254981000/How-sho...
https://www.afr.com/markets/debt-markets/why-the-rba-is-lend...
Bank of International Settlements is the central bank of central banks. https://en.wikipedia.org/wiki/Bank_for_International_Settlem...