Thanks for your question! With Yanfly Plugins, this makes the solution a lot easier. Using YEP Skill Core, you can set up a skill similar to this:
YEP Skill Core has the After Eval notetag which lets us put in code to check if the target is either Dead or at 0 HP after the execution of the Skill. If the condition is met then it will call the drawCards function from our Card Game Combat plugin to draw 1 Card. You can change the number of cards drawn by changing the number in the parameter of the function. You can also use this function as part of an Eval step in a YEP Action Sequence.
Once we get to Card Game Combat v1.4.0, we hope to implement some popular Card Keywords such as in this case Mortal / Lethal / On Death which should help with these types of trigger conditions. Until then, hope this workaround helps. Let us know if you run into any issues or if you have any further questions :)