When we went to the BAFTA'S a few years ago Nic was definitely booked to be there but he didn't turn up so like you say it's a 50/50 chance wether he will turn up at the Knowing premiere.
I see what you mean, so really Nic may not show up at all, being that it's sort of low key it's either 50/50 chance, he may or may not decide to turn up, I have a feeling that he won't somehow,
According to the Premiere Hub website the London premiere of Knowing is rated as average which means it's rather low key and there is a slim chance Nic will be there.
Average: These premieres are mainly the film stars and celebrities from the country the premiere is hosted in. An odd A-list may pop by, but don't expect too much.