They should play the way they recorded it, unless they are doing a live performance, but if they want a music video, how do they expect you to do a good job if they don't play it like it is on the Master track? Now you can use the different cuts to edit the video and create different scenes or whatever, but audio synching shouldn't even be a concern for you. I also currently only use one camera, we do multiple takes, but the artist always performs it like the Master track is. I mean all you have to do is ask the guys, "OK look guys, which version do you want people to hear?" If it's just a demo track they are using, they may not have figured out which version they want yet. The master version needs to be decided on by the band prior to the filming of a music video, not during. And then stick with that version.