Unity 3 support after version 4 release

Will Unity 3 be supported after version 4 release?
I mean if for example Apple updates XCode and iOS builds stop working. For example. Will it be fixed also in Unity 3?

Yes, they will support it at least for the entire 2012, as they said in THIS post of their blog.

As @mr-drayton said, this post of their blog explains it. You might aswell find useful informations on the dedicated FAQ for Unity4 on the official website.