Also, even if Bheeshma & Drona are distracted, how does Duryodhan get captured? His 99 bros are there to stand b/w him & Bhima, while Ashwatthama too is there. Who are they expecting to stop Ashwatthama - Abhimanyu? Dhrishtadyumna? Virata? Drupada?
About Yudisthir exposing himself, I guess it's an issue of whether Bhima kills Duryodhan first or Bheeshma captures Yudisthir first. But if it's a case of just attacking a defenseless Hastinapur, couldn't someone else, say Virata or Nakul have been sent there?