Coming from a pentesting background (and now working as a CISO), I can see both sides to this. tptacek is almost certainly correct in his characterization of the events, and I agree wholeheartedly with what he's said. It's important to note that this researcher didn't just chain several exploits together, but sat on sensitive data unbeknownst to Facebook in order to exploit other vulnerabilities later. Those vulnerabilities could not have been exploited without the initial (fixed) compromise.
Think about it a different way. If this researcher had found SQL injection in a webapp, dumped the usernames and passwords, and reported the vulnerability for a bug bounty, he should get paid. If he kept each of those credentials, and then logged into other systems using higher-privilege accounts that he'd compromised even after the SQLi is fixed, he is basically continuing the exploitation of an already-fixed bug. Those don't deserve payouts. Similarly, if he'd established some sort of persistence (such as a reverse shell, etc) on compromised assets, he can't keep coming in and getting more and more bounty payoffs. Fruit of the forbidden tree, in this case.
Where I disagree with tptacek is with regard to the benefit of bug bounty programs. Although I'm not currently running one, I find the idea fascinating and helpful for two primary reasons: first, you're almost definitely going to see generally better results in a well-managed bug bounty program (not necessarily something like Facebook's White Hat program) than traditional pentests or application security assessments. More eyes are almost always better when searching for tricky problems. Secondly, if you're a large enterprise, there are already people "testing" your security. I'd much rather be able to pay out a researcher than drive them to more nefarious buyers. You will probably encourage many people to test your security (which screws up metrics) but if finding security problems is the ultimate goal, it's worth it.
Even in this case in point, Facebook did discover an RCE that could have been (and kind of was) extensively exploited due to the fact that they held the bounty. If an actual malicious hacker had found that problem first, they would have been in significantly worse shape.