The problem with that sort of approach is that it isn’t thread or exception safe, and will be slow. As you go through the blackboard, all the minions you haven’t checked are still trying to get to you, so if something goes wrong with the dying minion you’ll get a bug, if any of the minions above where you are on the list copy their pointer value from any of the ones from below you on the list, you’ll get a bug. And what value would you be resetting to? If you change it to another minions pointer, what if that minion dies whilst you’re halfway through? If you’re changing them to NULL, you’re already performing checks with the askers, and IsValid will simply behave better.
The trick is to remember to check IsValid() any time the target could have died since you last asked.