If by 'defeat' you mean 'kill before the Last Battle'. It looks pretty certain that Rand's going to reach that, whatever happens.

The problem is that unlike before, Rand can now tell a darkfriend at a glance. Previously I'd have suggested a channeler behind a weave of invisibility who struck with balefire. Squish, dead. But now Demandred can't come after him himself, nor can he send a lackey. That leaves attacking those he loves - Min is pretty well protected, but Tam al'Thor is not. Kidnap him to lure Rand into a trap?

Actually Rand's greatest vulnerability at the moment is his warder bond (which is just one more reason why Elayne's recklessness is so selfish, doesn't she think?). Demandred doesn't know about the three of them, obviously, and since they didn't have the bond in the AoL he might dismiss it if he did. But it's the surest way I know of to kill Rand.