I don't know what your definition of significant is, but I think they'd definitely sell less tickets in that scenario. Like Jon outlined above, it'd be a drop in the ocean. It's next to impossible to get tickets to see a particular starter pitch, so even if people did buy tickets for the exact purpose of seeing Prior pitch, they were in for a crapshoot anyways. Not that I think that knowing about this before would've significantly impacted ticket sales, but there's another way to look at this. The overall ability of this team to compete is definitely hurt by injuries, especially to one Mark Prior. Some people (maybe not a significant amount) would be soured on seeing the team, period, with this type of news, regardless of who would be pitching the day they'd be going to the game.