Definitely from the descent of the Poggio on. and very possible between Cypressa and Poggio if Pidcock and MVDP play it smart and do token pulls. Not making it clear they ain't riding, but not truly riding all the same.I think Pogacar only does not ride if the other 2 are being too ostentatious about it between Poggio and Cypressa and that pisses Pogacar off. But even then he might still ride as it would still be a better chance than what he would have if the peloton comes back. From the descent of the poggio on it don't matter and they can make it clear they will only sit on his wheel. From that point Pogacar will for sure ride. Pogacar plan has been to light it up on the cipressa, then win from a small group. he does not want the peloton to come back. Add in how he has smashed the peloton often enough and that he been focusing on this race for months and i don't see why he would sit up if he is as strong as i believe him to be. I do not think pogacar won't have believe in himself even when pulling Pidcock and MVDP.
The gap in the end was 4 seconds. Only a couple of shorter/weaker pulls and Pogacar and Pidcock would be 7th and 10th in a 2 man sprint.
MVDP backed himself not to be dropped on Poggio or at least be close enough.
You talk as if Pogacar is the only one who needs to win the race while VdP's road season revolve around 3 races (and he is an outsider for 1 of them), so this race is/was his second best chance.
Pidcock in the same time finds himself in a group of 3(later 2) before basically a false flat like Poggio while he is the best sprinter (according to you) in the said group.
Both of them had all the reasons to pull and not play some silly games.
But hey, you think that Pidcock was the best sprinter and still ask why would he work, so I don't think you put any effort to look at the situation objectively.