on
Called when the multiblock is unformed (i.e., was formed before, but now is not). This includes when a part of the multiblock is unloaded and the multiblock becomes unformed because of it, or when part of the multiblock is broken/changed, and it becomes unformed because of it.
This is not called when the multiblock itself is unloaded, use PylonUnloadBlock for that.
partUnloaded is true if the multiblock became unformed because part of it was unloaded, false otherwise.