You might think that Mikhail Prokhorov would have had a not-so-soft case of buyer’s remorse this past spring. A month before the start of the National Basketball Association season, the 45-year-old Russian billionaire struck a deal to buy the New Jersey Nets from the real estate developer Bruce C. Ratner. When the league owners finally ratified the sale eight months later, the Nets record stood at 12 wins and 70 losses, and Prokhorov’s shiny new team was the laughingstock of the NBA