My own view is that if Tory MPs were asked to vote solely upon who they wish to see as PM, Boris would win easily.
However I suspect that many/most of them will be thinking ahead to the next election, with the real question in their minds actually being "Do we stand much hope of winning if Boris is still PM?". Even some of Boris's biggest fans might vote against him if that's the way that they're thinking, so I think that he might well lose the vote.