During the close combat phase, enemy models fight the crew and attached characters as normal. The machine itself does not fight back. A war machine that is attacked in close combat is assumed to have a W of O and is therefore hit automatically. Resolve the combat as normal. If the machine has no crew left to defend it at the end of a combat (because the crew fled from the charge, have broken from combat or are wiped out), the enemy automatically destroys the machine, and is immediately free to pursue the broken crew or overrun as normal.
A war machine's crew can automatically choose not to pursue enemy breaking from combat if they are still crewing their war machine (unless under the effects of Frenzy or Hatred). If they choose to pursue, they will abandon their machine and pursue as normal.