He can have been really ill and is still recuperating and his health should come first.
That also doesn't mean to say he (or his puppetmasters) won't delay his return longer than necessary so he returns when they have good news to shout thus psychologically distancing him in the minds of the electorate from the worst days but associating him with the good ones, making him look like a white night. He can then throw one of those filling in under the bus for poor performance (almost certainly Hancock) to look like he's taking action.
We will have to see when he returns but I do think it will just happen to coincide with good news.
Or if Cummings has it maybe he's not allowed out until daddy is there