I don't think RJ planned the specifics of the gholam's demise. It reeked of Sanderson trying to be "clever" in the exact same way that Graendal survived. It was written like an early mystery novel, in the wrong voice with the wrong narrator--Mat knew all along the plan, but we didn't even know that he had a plan. Brandon wanted us to say, "Ha! He had in planned all along, how clever!" That's not how the WoT narrative keeps secrets from us, and it feels really unnatural. RJ didn't resort to these mini episodic mysteries to give us a sense of "action," and I much preferred it that way.

IMO, the gholam should not be able to pass through a gateway, but I don't think RJ yet decided how he'd have it die.

I think the more interesting question is what the Shadow wants with Matt's medallion...