If you notice that a prominent member hasn’t been active in the community recently, drop them a line. Send them a private message or an email. Make it known that they are missed, and make sure everything is OK. Don’t just sit back, hoping they’ll come back one day.
Maybe they’re having trouble with the site. Maybe they’re feeling disillusioned with the community. Maybe they’re having a tough time in their personal life. Regardless of what the problem is, it pays to reach out to them.
You’ll make them feel special and you’ll remind them of just how strong the community is.