Looking up Terrence Howard, I stumbled upon this silly MTV Movies blog entry:
http://moviesblog.mtv.com/2009/07/29/bryce-dallas-howard-youre-not-alone-here-are-five-other-re-cast-roles/Apparently, one of the bad vamps from Twilight is being replaced by Bryce Dallas Howard in the third flick. Anyway, it talks about other film replacements.
Maggie's Rachel Dawes was sickly little mess, so I don't think it's a good example at all. Hardly an "upgrade". Michael Gambon is an excellent actor, but Richard Harris was a far better Dumbledore. Hardly the "definitive version".
All the "Batmen" aren't a good example either IMO. It would've been an example if Bale had been replaced in the second film like Katie Holmes was. Maybe when we went from Michael Keaton to Val Kilmer to George Clooney. But they include earlier Batman actors
and Bale in this. Bale's Batman movies are a fresh take and in that vein, Bale has never been replaced nor actually replaced anyone. You can't argue Bale replaced George Clooney when Bale's films are a reboot and came eight years later.
It also lists Terrence Howard being replaced, which is stupid because Iron Man 2 isn't even out yet. I doubt Don Cheadle would fuck it up, but it's definetely not "proof enough that [Bryce Dallas] Howard's upcoming gig might work out for the best."