The language has changed & the way things were done (i.e. drag/drop form, create a macro, modify a few line & you are done) will also change.
It won't remain a tool, which a non-developer will find easy to use.
Object model should remain same for basic stuff (Workbook, Worksheet, Range) etc.
New set of things will get added & that will change the object model & hence new learning (e.g. Ribbon Interface)
Not to forget, .net brings in its own concepts/complexity.
I'd suggest that VB6 wasn't killed suddenly. Official MS support, perhaps, but still the community is alive for both VB6 and VBA here on SO.
As with any technology with a WIDE user/customer/3rd party vendor base, it will take a long time for VBA as a scripting technology to fade away. I would imagine that it will take years for its successor to fully overtake VBA.
It will die, IMO, but not suddenly. Excel used to have a macro language called XLM - basically a keyboard playback on steroids. XLM is still supported, and there's easily a dozen people who use it. That's why I think VBA will be around for quite a while. It won't be updated, supported, and maybe not even acknowledged, but it will be available.
Sooner or later MS will integrate .NET with Office apps and fewer people will care about VBA. Right now, I can put some VBA in an Excel spreadsheet, send it to a client, and deployment is done. I can tell the IT department it's an Excel workbook with macros, and they don't feel threatened because they don't know any better. When .NET has deployment options that simple, I'll use it instead. That day will come and VBA will slowly start fading away.