The nylon webbing should be good for a long time if kept out of the sun. Many have a shock absorber sewn into them so if you fall it tears loose reducing the shock. If you ever fall wearing your harness, they recommend replacement.
When I taught hunters ed, I would ask anyone who hunts elevated without a harness if they were willing to stand 2' up on a chair, put their hands in their pockets and fall uncontrolled to the floor. ZERO takers. So WHY does anyone think gravity from 8-10' up or higher will hurt them less? I won't hunt elevated without a harness, and none of my core hunting buddies will either.
There really is NO reason not to be tethered with a harness from the time you leave the ground until the time you get back down.