There is not a great deal written about the actual death, but there are a number of places where folks that care for Fodder-wing are very concerned about him.  Jody always hears these and keeps thinking that there will be time to see him at some point, but the worries get more and more common and widespread and when he finally goes to see him, he has already passed away.

There is a brief description of the actual death, once Jody's father comes down to check on him.  Apparently he'd been hurting for a couple days but seemed to be on the mend, when they went in to find him having passed away in the night.  Thankfully for Jody, he'd already named the fawn.