The model cannot Pursue, Declare Charges or Declare Flee as Charge Reaction. Characters can never join units with War Machines, and Characters with War Machine cannot join units at all.
When a War Machine fails a Panic Test, instead of Fleeing it is Shaken until the end of the next Player Turn. War Machines that fail a Break Test are automatically destroyed. War Machines and units Engaged in Combat with them cannot make Combat Reforms.
When a unit charges a War Machine, it can move into base contact by having its Front Facing contact any point of the War Machine's base (it must still maximise the number of models in base contact, see subsection II.1.A “Bases and Base Contact", page 4 and Figure 1 page 4). No Align Move is allowed. Ignore the War Machine's Facing, as it does not have any due to its round base.