He thought the Cruz Amendment would pass, and it could have. He needed to fleece just one Moderate Darling, which he was able to do with massive Opiod funding. The question is whether McCain's surgery had an impact. It certainly delayed the vote. If McCain didn't leave, BCRA could have passed with 50+Pence. Unless my timeline is off.
Ultimately I think that the killing blow has to have been the leaked reassurances to the moderates. If McCain's surgery was all it was, then they would've had to go another round of "terrible score-> tweak small stuff -> rushrushrush," but Johnson and Lee pulling out the way they did basically cemented the fact that it wasn't possible to get enough Senators on board all at once.
Of course, the reason WHY those reassurances leaked is its own kettle of fish. That'll be attributed to McConnell not having the right leadership tools to actually legislate
for something. Against, sure, but he wasn't capable of providing motivation absent a Democratic president for him to rally against. Not without alienating as many people as he brought around, anyway. By the time he got around to trying to sweet-talk the moderates they'd become sufficiently aggrieved to tell both news outlets and their conservative colleagues about the promises he made.