Doug Ostrover and Marc Lipschultz seemed to have private credit figured out. The executives joined forces to launch fund manager Blue Owl Capital, turning it into a powerhouse in the booming business of lending to private companies without the use of banks. They pounced on trends early, zeroing in on lending to software companies, plowing money into artificial intelligence and selling their funds to wealthy individuals. Ostrover and Lipschultz became instant billionaires, buying a hockey team, a piece of a football team and luxury real estate. Now, the foundations of their empire are cracking—raising questions about the once-sizzling industry’s future…