So basically, if I understand it right, the main thing was when someone told him about flare and hunter's mark in the hunter's hand after RDU already had the match pretty much already won. And that there was no way at all for RDU to lose?
If that is the case, I really don't think it would be fair for RDU to have to replay an already won match.
He had 1 life and a Ice Block. Amaz had been holding onto a card the entire game. It was Hunters Mark but could have been Flare.
RDU had an Alexstraza in hand. He has 2 choices here. Play it on Amaz and win next turn, or play it on self to stay alive if that card in Amaz's hand is Flare.
He played it on Amaz.
It should be noted that he played it like almost immediately when he got the message. So I think he would have made that play anyway.
And even if he didn't and played it on himself for the life gain instead, he had a big advantage. All Amaz had was the Mark in his hand and a bow equipped. No more cards in hand and no minions in play.
RDU would have had a Azure Drake and Alex on board. He also had 2 Fireballs in his hand, a Pyroblast, 2 Frostbolts, and a Ice Lance. He wasn't going to lose either way.
The problem is not whether RDU used the information to make a game winning decision. It's because the game was clearly compromised and it still counted.
In any competitive game worth its salt, any such outside interference is handled with a rematch, a loss or disqualification.
But this is what I agree with. Just for the integrity of the tournament and to stop all rumours and stuff, they had to start over. It would have been unfair to RDU if he lost in the rematch but that would be his friend's fault. Now we have RDU's name being dragged through the mud because DreamHack mishandled the situation I think.