Do you mean "possibly hit"? How he leaves office is a big question mark as there are two factions who want him out for different reasons: if he goes because too many have died and the overall handling has been shambolic in the "everything done late/half hearted" sense, he'll probably resign on his own accord once the vaccine rollout allows most if not all restrictions to be lifted. If however he doesn't lift them quick enough for the CRG's liking and the fallout from all this becomes very apparent while Johnson is still in charge, his departure will more likely be through "resign or we'll kick you out" from his own party.
From a deaths' perspective I don't think there's much more that, for a while at least, can now be viewed in similar light to today; above 100,000 landmarks are fewer and further between (I'd say 150,000 is next), and the peak death rate appears to be coinciding with the 100k, so if it's all going down from here any "alarmist" media reporting will be plainly obvious.
The peak in infections was on the 8th January, so by virtue of the "deaths within 28 days of a positive test, they'll be falling by the 5th February at the latest, but as 28 days is the end point, not the start point, they may well fall earlier, but the rate could well be falling rapidly in the week or two leading up to the mid-February review, given how rapidly it appears to be dropping right now.