The only time I ever replaced a pillow was after I lost it. That was over a year ago, and I still have no idea how that happened or where it went. I keep hoping this pillow will last forever, but I suppose I’ll replace it whenever it becomes uncomfortable. It only cost $5, so it’s bound to happen eventually.
As far as whether feather or man made last longer, I have no idea. My mother got me a feather pillow when I was little, and I couldn’t stand it (I felt like I was suffocating because my face would sink down into it, and the ends of the feathers were sharp when they poked out!). It took me a few weeks to convince her that the pillow made sleeping miserable, and she replaced it. I still can’t stand feather pillows, so I’ve used man-made ones ever since.