As you say, not all drills can be covered in the checklist. In the R22, there are three possible scenarios:
1/ Big bang, engine destroys itself and smoke enters the cockpit via the central console. Enter auto and put off the battery (if time) when finished with radio and intercom. Purely to obviate sparks if you make a big Horlicks of the EOL and hit hard/roll over. Remember the tank and fuel lines are above the engine.
2/ Lots of oil smoke in the cockpit but engine still running. Low powered descent and powered landing asap. Colleague experienced this and said difficult to see and breathe in the cockpit. Battery and generator off rather irrelevant in this case.
3/ Cockpit electrical fire and huge volumes of choking poisonous smoke. Really nasty in the cockpit. Battery and generator OFF and land pronto. Unfortunately the person who experienced this said that the wire insulation continued to burn well after the electrical power was turned off.
Note: It seems that the airflow from the engine bay and any smoke there from flows forward and somehow enters the cockpit in the R22.