Thanks, alak, for your interestin Rae/Roy.
I don't see it quite the way you do, Helen.
The Rohan group were in this for Amroth (Mellondu). As for Ĉdegard, Béthberry's admonition of a "meant-to-beness" (or something to that effect) stuck with him, and he is in this to follow it through. I think it's the same for all the Rohan group, that they're in to help Amroth find Nimrodel....it's what he's been talking about since the get-go.
The Gondor group's task is the one that's ended: Mellonin and Mellondu are reunited... but Mellondu has this Elf spirit inhabiting him, and that will affect each Gondor group character according to their lights as individuals and as characters.