7 years at any organization is a long time, and with so few rungs above him on the ladder, it is only reasonable that he'd move on to something else.
If you're not learning anymore, it's not fun anymore, or you're not having the effect you want to (or any combination of those), its time to leave.
I (non employee; student+volunteer) certainly do this. I've drifted between open source projects and communities, reducing participation drastically when I find something I learn from more. Im pretty involved in a couple projects and I really want to stay because they're awesome, but it's quite possible that in a few years I'll be somewhere completely different. At the moment, I hope not. But only time will tell.