If the VG is varied on, the task would fail because the first step the task does is rmdev -dl <hdiskNN>, as the disk is still in use, the rmdev would not work.
If your VG is varied off, then nothing is in the way to remove the device, so it would get hot removed. You would then have a missing PV in your VG when you try to varyon it.
HTH,
p5wizard