It would fit in all sort of ways.

Imagine how pissed off Mat would be to lose the only thing good he considers to have gained from the Finns... shortly before he has to return there. That would have a very Jordan feeling, it's the sort of combination of heroism/chivalric sacrifice and humour he liked to have for Mat.

If he does kill the gholam to save Elayne, this adds a layer of irony. He gives up the medallion to save an Aes Sedai.

And if it's Elayne who destroys the medallion to kill the gholam - a medallion she died to study and that Mat would have given her for her protection against the gholam while he's not around because he feels guilty by coming near her again he's put the gholam on her trail once more, that's yet another sort of Jordan-style Mat humour - this time in the "oh crap, what is Mat gonna say?" vein.

The medallion is also a "one-eyed fox", so maybe giving it up is the meaning of "giving up half the light of the world", though that's a very dark horse idea... unless the medallion is used against the gholam while Rand is with Elayne, I guess. Still, I don't think the fact the fox of the medallion has only one eye open is a pure coincidence. I think there may be a correlation between Mat losing and eye and his one-eyed fox medallion (could be just a motif, though, because the Foxes are involved in how he gives up an eye, or the reason why he gives it up).

You have a point about the dreams, but I doubt it's very important (in the sense that I don't think Jordan planned for the Shadow to use Mat's dreams until the end, when obviously Perrin is already going face some of that again, and Egwene must have some TAR stuff ahead - though I'm still unconvinced in her case it will be about fighting there and not all related to mastering her Dreaming talent instead) Jordan never even saw fit to give us the reason why the Shadow wasn't visiting Mat's dreams anymore (in the series, I mean), but if he intended him to lose this protection and this would be relevant to the plot, I don't think he would have revealed in a Q&A that his protection was the medallion. That's precisely the sort of possibility he RAFOed just in case. This could speak against Mat not losing the medallion, but also that his dreams are simply not relevant in the series anymore and Jordan already knew that and saw no reason to rafo the fact the medallion was his protection.

One last source of humour in the destruction of the medallion is all the AS Mat has pissed off with it. Egwene, Nynaeve, Elayne, Joline - and Tuon too, even Moiraine. Having him with no protection, fearing Elayne etc. will reveal he's lost the medallion could bring one or two funny moments.

The medallion isn't all that useful to Mat or anyone else for the LB either. As we've seen at the Cleansing with Alivia, if Mat has to face an AOL channeller on the field during a battle, it would take about 10 sec. for them to figure he has a weave breaker and how to work around that to kill him. At best, this could buy a few vital seconds for Mat to vanish (eg: step through an open gateway) or if he's already moments away from killing the Forsaken (though I'd say the odds that he gets anywhere close to Demandred etc. in battle are really really low... they'd far more likely face each other as generals, with a whole battlefield between them, and the only way Mat stands a chance is if he has the "mixed gender" groups who know very destructive weaves under his command at that point.. which I expect he will have. He's only begun to use channelling in his battle tactics, IMO - we're far from having seen the last of that with his use of Teslyn against the Seanchan - that was merely an appetizer to make him think of how he could use the OP in battle.).