This WU tells me this essentially:
Even if his legion members are alive and he is prevented from revival, then we can win. However, even if we take care of all the legion but fail to prevent Sargeras' revival, we lose.
Essentially, we should be able to lynch Cal or postpone his revival with a lynch even if Polar is going to revive again.
Because it's not about Polar coming back, it's about preventing Cal from being summoned.
Unless I understood this completely wrong.