In 1966 Paul McCartney fell off a motorbike, broke his neck and, despite dying, ended up playing in a basement with the band yet to be known as The Band in Woodstock which is in Oxfordshire.
The bereaved Beatles decided that, rather than give it all up out of respect, that somehow they would bring in an exact replica to replace McCartney but would also put in odd clues on their recordings. In 1969, the story broke and thousands of Beatle fans played the records forwards, backwards and sideways, approach the sleeves from all angles and argue over the voice. Eventually, Paul/his replacement had to deny it all. In some quaint areas of Beatles scholarship, the conspiracy lives on.
Why bring this up? Because conspiracy theories have a life of their own and no matter how one smacks them down, like a sponge separated in its constituent cells, it can regenerate in a different shape. Conspiracy theorists, on the other hand, just keep getting weirder and weirder as they cling to the wreckage of their cherished belief. Some change, see reason or whatever, but those are few because a stigma seems to attach to people who look at evidence and see how wrong they've been all this time. They lose a strange kind of face. They become non-entities.
I never went through the Paul is dead thing. For a start I was too young. I had a real dead Beatle in my teenage years and kept politely apart from the conspiracy theory that grew up around John Lennon's stupid murder. People can't see something with no apparent logic behind it without trying to impose some sort of human agent reason for it. Why would a conspiracy be needed?
When I began teaching the favourite science question of the children was "did NASA fake the moon landings?" These usually got a curt no from me before moving on. But some children were more obstinate, demanded more of my time by asking the same questions, the usual ones. When I offered to go through the evidence with them, they generally declined the offer. I won't claim an original observation here but this is something I find all the time. Someone says that they are skeptical of X when what they really mean is that they have decided X cannot be true and therefore no evidence you can provide will change my mind, mostly because I am not going to look at that evidence anyway.
Science deniers of all persuasions do this. The science bit doesn't matter because the science is going to ignored anyway, or treated with a strange invalidation process that requires a minor point of possible invalidation and then magnify that, proclaim that it is part of a debate. Except that the science does matter. It bolsters the denier case because science is so powerful.
But that's only the case if the science is used in the correct way. But the science denier uses bits of science in an incoherent way to support their case, cherry pick bits of science, portray their case in the best light and the real science in the worst light. And the conspiracists believe that the failure of their idea is further proof of the conspiracy. But I'm sure you all knew that.
Paul is alive. The evidence is pretty clear. The evidence to prove otherwise is not sufficiently elastic to actually prove otherwise. The consensus, then, is that Paul is not dead, and it is a consensus because the evidence has persuaded enough people to make it so. The evidence.