David Cohen has today's great post up titled The Boomerang Founder.  He defines "the Boomerang Founder is the one that “throw away” but then comes back later on and hits you upside the head, often causing significant trauma."

"You start a company, and you and a couple of buddies get together and draft a simple email about who’ll own what. You name the company, and maybe you even incorporate it. You’re in business!  Some time goes by, and one of the founders isn’t work out or takes a day job or loses interest. Maybe she’s just not a startup person, she realizes. Now you’ve got one less founder, and you’re down to two at this point.  It feels like no big deal. A buddy is departing - it’s all good. They’re good people."

... "Boom"

Read the story.  I've seen it more times that I care to recall.  David has some very practical advice for all founders at the end.