Outstanding. Using "jumped the shark" just never felt right for this situation. "The elves have left middle earth". A spot on perfect description of this sad and awkward phase all startups encounter as they grow to successful bigcorps. I love it.
There is also a potential that they have a great idea related to your company that they pursue once they leave.
When morale is bad, people who are left tend to offer you resumes when you quit. In that situation I've been glad to forward resumes of people who are good, and have avoided forwarding resumes of people who aren't. (After all you get judged by the quality of people that you recommend.) To the extent that I'm someone people want to work with again, this results in cherry picking the best people.
The effect is even more direct when employees go through recruiters. Recruiters ask about the work environment where you are, and have no problem trying to track people down if they get the sense that good people may be available.