One thing that really boosts Johnson in his current position is that there is no obvious person there to replace him as we see from the betting chart above. This of course all changed with the massive decline of the Sunak in March and since then no one has really emerged to perhaps take his place.
As can be seen in the betting there are 5 contenders who are rated as having an 8% or greater chance of becoming the next leader but the top one is only on 12%. Tugendhat is the current favourite by a small margin but he is never going to to rely on the patronage of the current big dogs in the party and I doubt if he wants to. When Johnson eventually goes my guess is that Tugendhat will play a big part.
As to what will bring Johnson down I wonder whether it won’t be the Sue Gray report or something similar itself but rather a clumsy attempt by Number 10 to cover-up certain aspects.