Our project currently uses the very old Java Studio Creator framework and now has new requirements and plans for future deployments which require the application to finally remove JSC and migrate to either 1.8.x or 2.0 of IceFaces. A migration to 1.8.x seems to be the safest and most reliable option to take to me. Would delaying and not taking on the challenge of a migration JSF 2.0 make sense or should a migration directly to IceFaces 2.0 be used instead?
That <webuijsf:xxx> component library is called "Woodstock". Now you have new and solid keyword. ICEFaces was officially been pointed as recommended replacement of Woodstock projects when Woodstock was officially been abandoned and discontinued.
I personally recommend you to just take the ICEFaces migration path. It's well documented. Also, when you migrate to "plain" JSF 2.0, you'll have to redo the entire look'n'feel as "plain" JSF components does not ship with any bundled CSS. Going to ICEFaces 1.8 or 2.0 doesn't really matter that much. To take advantage of new JSF 2.0 features behind ICEFaces 2.0 you'll only have to change a lot of other things afterwards, but even without that, you should already have a working project.