How would they do?
Extremely well. They're pros.
If the intimation is they wouldn't play well if they didn't have perfect conditions, thorough knowledge of the course thru practice rounds & yardage books, well, maybe they would lose a couple of strokes in the course of a tournament, so instead of say 15 under they would shoot 12 under.
Remember, the whole reason they have that kind of access to that information (which, presumably we amateurs don't) is this is their livelihood. It's their jobs, their careers. It's like saying what kind of job would a master carpenter do without a blueprint to a house he's building or his favorite tools. The carpenter would still do an extremely good job...they're master carpenters.
Pros are still the best players on the planet, and they would still score better than anyone else on the planet. Maybe not as low as they would with all that information, but still better than anyone else could.
So I guess the question is, how much does local knowledge & research (re practice rounds) help their games? I'm sure it has an impact. But it's one thing in knowing it's 193 yards to the pin & quite another to hit the ball 193 yards, ten feet from the pin.