It can function without him until his mum dies. And if he dies before his mum then William steps in. I despise Johnson but totally agree he should have been tested regularly, he's running the country (of sorts) and is at the centre of our response to the virus. I am ambivalent regarding the monarchy generally, but I don't believe anything would have been any different regarding the coronavirus crisis in this country for him having been tested. At least if a doctor who is currently isolating had been tested then they might have been able to go back to work and treat someone. That is what I call making a practical difference.