As far as I know, the closure of Armageddon is only a rumour. A Narnia attraction has certainly not been officially confirmed.
Should the attraction close and be replaced by a temporary Narnia walkthrough, you'd have to imagine that it'd be gone forever. The ride has very few fans and suffers from a horrible waiting area and pre-show.
I for one will be glad to see it go, to me it symbolises everything that was wrong with the studios when they first opened.
More info here:
http://www.dlrpmagic.com/today/2008/06/13/armageddon-to-be-averted-by-narnia/