I'm pretty sure you CAN do offline installs. Look around their site I'm pretty sure I read it there somewhere.
Also, I have the brushes kit and it does upgrade when you do the AD2 upgrade. All the paks are upgraded to the new version with AD2. One last thing, AD1 will still be supported for the time being. How long that is I don't know.
It was interesting programming the brushes. I've played drums lots of times but never the brushes. I learned that you have to start sweeps ahead of the beat, either by an 1/8 note or 1/4, depending on the sweep.
Personally, I think it's worth the upgrade price because it sounds so much better. I even saying this and I'm stuck not using AD2 properly because the individual outs aren't working for me at presend. I'm stuck with the main outs only.