is the (clear) winner of ward/kovalev rematch still pfp king?

Yes, just like after their first fight. I would have the winner at the 1 spot. The loser at 2, 3 or 4.

If it is a very clear win, there is an argument to be made about the winner being pfp no 1. If Ward outbox Kovalev like 10-2 or Kovalev KOs Ward, I won't mind the winner being pfp. Another scenario is if it's a much better fight than the first time. For example, if Ward wins without Kovalev gassing after 6-7 rounds, or if Kovalev wins despite Ward being elusive and doing his best to disrupt a clean fight.

That depends on who's list you are talking about. No two people have the same top 10 best pfp lists. It's just opinion and can almost never be proven right or wrong. I thought Kovalev beat Ward and Ward had done nothing special in the last 5 years before he fought Kovalev. I don't rate him on his great success in the super six tournament because PFP is supposed to be about how good you think a fighter is today based on recent fights and not fights of 7 years ago. I have Kovalev at number 4 and Ward at number 8. It's unlikely that a clear winner of the rematch would become my number 1 unless they win in an extremely impressive fashion.