In normal times an exhausted and ill PM would have delegated a lot and eased his workload whilst he concentrated on getting himself well but these are not normal times and he has had to be front and centre in the worlds spotlight whilst being extremely ill.
In normal times a sick PM would resign - Macmillan, Eden. In Macmillan's case it was a tired Government beset by scandals e.g. the Profumo affair. In Eden's case he'd made a complete mess with Suez, so he knew the game was up. Eden especially had been popular and successful before that.
Both then went on to live for another 20 odd years.
But these are not normal times and Johnson will have to be carried out kicking and screaming, not because he's got no-one to delegate to, although having kicked out the decent MPs from the party, there is an element of truth there, but because he's power crazed. Carrie too will want to enjoy her new wallpaper.