That variable is not part of the plugin API itself, what you do with it is up to you.
If you have no looping or long-running elements in your plugin, and thus have no need for it, you could just remove it entirely; it is not required by VoiceAttack itself.
If you do have those elements, you'd want to make sure that each of the instances that need to make use of that variable, have actually stopped, before resetting the value(s) that are used to stop them.
Having something independent like a call to VA_Invoke1() reset it/them may not guarantee that everything has come to a stop yet, depending on what your plugin actually does. That is for you to know and understand.