Conversely, you could dispense with his services at the most opportune time (say the next six months) and then have him and Hancock serve as scapegoats for anything the pandemic inquiry finds. As much as the Conservatives are going to be in a pickle, the Opposition will have to be sure about what they (the parties) really want, too. Better to stomach a lame duck prime minister and two years of internecine warfare, which could lead to a Conservative defeat in 2024, or better to face a fresh prime minister at the polls in 2022/2023?
The latter is inevitable now. If he doesn't resign then he'll be eviscerated by the local elections in May, and get knifed by the Tories then.