Give your insurance a try. Just tell him it had a crack that was not a safety issue so you never replaced it, but the crack expanded and is now a safety issue. I would bet they'll cover you, but only if you tell them before you have it replaced.
I was camping with a friend a few weeks ago and on the way to the campground he took a huge chunk of concrete in the windshield that fell off a truck. He called his insurance from the campground and they sent out Safelight Auto glass the next day to the campground and the guys replaced the windshield while we all sat around drinking beer and watching.
