Some questions.

1. You think that Gawyn will get his hands on Mat's medallion and use that to counter Rand's OP advantage. However is this actually required?

I mean Rand's channeling sickness has advanced to the point that grabbing hold of the power nearly knocks him out. So long as Gawyn surprises Rand even slightly, he could certaily kill Rand without needing the amulet, while Rand was still throwing up. And I don't know if Rand truly knows how utterly stupid/insane Gawyn is so he likely won't grab hold of the power before meeting him, especially if the meeting happens in a public place like Caemlyn.

I figure the sickness is caused by Rand's link with Moridin, so I doubt his return to sanity will have cured this, so unless Gawyn's attack happens after Moridin is dead, the medallion will not really be necessary for Gawyn to kill Rand since Rand will be unable to use OP to defend himself anyway.

2. Gawyn being able to kill Rand presumes that Rand is alone. I would expect that after his revelation at the end of TGH, he would go back to his allies and friends. If so Gawyn might well be able to win against Rand, but can he win against the Aiel/Aes Sedai bodyguards. Especially people who know how to get past the medallion.

3. For that matter do we know for sure that Rand could not get past it? I mean he has LTT's memories at this point, and he also knows about the medallion and what it does. He has also seen Mat die by a lightning strike from Rahvin so he knows full well its weaknessess. I figure if Rand has even a little time, he will be able to realise how Gawyn is protected and take him out anyway.

Ofcourse it is possible that Rand will be utterly surprised and won't have any time to attack Gawyn with indirect weaves, but again in this case the medallion won't be required anyway.

4. Would Cadsuane&Co really let Rand stay dead? I mean presumably her knowledge of Balefire means that she knows how to weave it. Even if Gawyn does manage to kill Rand, why would Cadsuane not zap the idiot and bring Rand back? It is certainly worth the price considering how important Rand is compared to the nobody that Gawyn is.

5. And just to throw in the possibility, if nothing else, Rand could use the True Power to kill Gawyn. The medallion being designed to counter OP would likely do nothing for that. I am unsure if the new and improved Rand would be willing to use TP again, even to save himself, but the option is there.