If you asked me this-morning, "Who can Linden Lab least afford to lose" my answer would have been simple: Cory Ondrejka and Robin Harper. At least (sitting on the outside here), every other member of staff seems to be replaceable.
For better or worse, Harper and Ondrejka appear to form the basic core that gives Linden Lab, and thus the Second Life grid its shape and core operational parameters. Linden Lab is what it is more because of Harper and Ondrejka than the contributions of any single individual or pair of individuals.
That's not to say neither of them can be replaced, but those two individuals form the fundamental direction of Linden Lab - whatever the goals are, whatever the strategy, they've made both strategic and tactical choices that have shaped Linden Lab as a company and culture, and Second Life as a platform into what they both are today.
Changing either or both of them is going to be a dramatic change. I'm not going to tell you that Ondrejka's departure is necessarily a bad one or a good one. Two highly creative and motivated people may produce brilliant work, but simply be unable to do so together. So it seems, with Ondrejka and Rosedale.
What we can say is that it signals a major change in direction for Linden Lab as we go into 2008. Ondrejka's next career move could mean a profound change of direction for another company as well. Both remain to be seen.