Wounds must be recorded separately for the rider and his mount. If the mount is slain, the rider may continue to fight on foot if you have a separate model to represent him. If the rider is slain, the monster might behave in an erratic fashion.
If the rider is slain, the monster must immediately take a monster reaction test: take a Leadership test on the monster's own Ld. If the test is passed, the monster fights on as normal. If the test is failed, roll a D6 and consult the monster reaction table below.
Regardless of the result of the test, a monstrous mount that has lost its rider must always use its own Leadership for any Leadership-based tests, even if it is within the army General's area of influence (see the Generals & Battle Standards section)
If a stand & shoot reaction kills the mount during a charge, the model is replaced by a foot version of the rider and the model does not move at all, as the rider frees himself from the monster's harness. If it kills the rider, take the test for the monster and then finish the beast's charge if possible.