ISIS militants posted the gruesome execution video Tuesday on YouTube
Dick Costolo, the company's COO -- who appeared in late September at TheWrap's Grill conference -- will replace him
From TheWrap's entertainment and media conference Monday and Tuesday, TheGrill: "Why Social Networking is a Game-Changer"
Dick Costolo and Jeff Weiner on monetizing digital technology
"The predominant 21st century media company has yet to avail itself ... it will succeed at leveraging social media and optimizing content"