On the afternoon of Dec. 9, Marco Morelli, chief executive officer of Banca Monte dei Paschi di Siena SpA, was preparing for a board meeting in the lender’s Belle Epoque-era offices in Milan when the news hit: the European Central Bank had rejected his bid for more time to raise the 5 billion euros needed to stay afloat. The gathered executives and their advisers from JPMorgan Chase & Co.