One has to assume Celene is smart enough to groom a successor, since it is highly unlikely she'll have children given the rather absurdly telegraphed hole in her armor. Probably one of the many young nobles she had educated to a pro-elf mindset at the university. She's basically educating the entire next generation of nobility to look more favorably on elves, and it was working.
One cannot assume that such a plan would work, especially not now that so much blood is being shed. Any of hope of the long game's reliability, which was faint as hell to begin with, has evaporated.
*sigh* So Merrill's skill is there for gameplay reasons only you're saying? Even then there's still shortcuts.
Wrong. Merrill flat out says one of the paths has been blocked by a landslide (the shortcut in fact) I'm pretty sure in six years Marethari could've had that cleared out (even if LOL maps didn't show it).
Merrill's skill is short-ranged. And the maps do change; in fact, if you go up to the top of Sundermount in Act 2, you'll see that the blue barrier is gone and replaced by an overturned wagon (which, by the way, strongly implies that someone had been there three years before she was allegedly possessed...), so if Bioware had wanted to show that the landslide had been removed, they'd have shown it.