i dont know if its mandatory to remove the A-pillar trim to replace the windscreen. but mine also got cracked and from what i can see from the crack, it is a very thin piece of plastic, so if the windscreen is a tight fit, and someone tried to pry it up to obtain a little more clearance, it would probably crack. in my opinion. there is also on this site an exploded view of the trim and how to remove and replace it. there are at least 3 screws holding it, along with a bunch of snap buttons, 2 of the screws are hidden under the window weatherstripping, the third is under the B-pillar trim. not sure how much your will cost if you want to replace it, but mine from the dealer is $368.00. someone on here put me onto
http://www.everythingnissan.com and they have the piece for $280.00. i am going to change mine in a couple of weeks, just to ensure water doesnt get under it and start the A-pillar rusting. hope this helps, good luck.