It’s a situation of mutual dependency. They wouldn’t be where they are without his electoral appeal, and he wouldn’t be where he is without their continued support, which is why he will continue to curry favour with enough of his MPs to ensure that their level of support doesn’t drop to the point where he is removed.
The bigger question is how long the English electorate lend him their support. Much of what he says still appeals hugely to the English public (levelling up, reducing taxes, tackling immigration), and if enough of them think that his achievements (getting Brexit done and delivering vaccines) are evidence that he could yet be successful in those other areas, they may be willing to pay out more rope. However, if by 2024 those areas have not seen improvement, then that rope will be a noose.