Curiously enough, it doesn't! The dispel simply vanishes, as if dispelled itself; nothing advances on the Merrow, but nothing retreats on it either.

As for the communication thing... Yes, actually. It doesn't have very many actual words though - most of it is feeling-based this late in the stages of infection, and those feelings are anger, bitterness, resentment, and a desperate hunger that can't be quelled.