Addictive Drums 2 - When all track outputs sent to Sonar...

I'm not an AD user, but this applies to all virtual drum instruments...
 
The sole function of any drum sampler's master bus is exactly what you suggested: for doing all the mixing within the instrument and routing the whole thing out to a single stereo track in the DAW.
 
Personally, I prefer coming out from the instrument's busses to individual tracks, e.g. grouping all the toms into a common bus within the instrument's mixer, then sending that tom bus to a "Toms" track. That yields the best of both worlds, plus it allows me to freeze the instrument and still be able to tweak effects afterward.
 
I don't think I've ever had a need to use the master bus in the drum sampler's built-in mixer. I suppose you could put a compressor on the master for parallel compression, but that seems like a very clunky way to go about it. 

That seems like an oversight on the part of XLN. One of the things I like about Superior Drummer is you can apply its effects to individual instruments or to any of its 32 busses. Even Kontakt-based drums can do that, albeit somewhat less conveniently.

I by pass the mixer entirely, so send all the outputs except the master and effects. I've hidden some of the others though. I prefer to use the same sets of reverbs for everything, though having access to the room mics mean I use little reverb. I like to have access to the drums faders when mixing the other elements, so having them all in the console view suits me better. 
 
To do a New York style with the master outs, I'd have to mix both in and out of AD2, so the masters had a mix to work with. That's too fiddly for me.

Kamikaze
I by pass the mixer entirely, so send all the outputs except the master and effects. I've hidden some of the others though. I prefer to use the same sets of reverbs for everything, though having access to the room mics mean I use little reverb. I like to have access to the drums faders when mixing the other elements, so having them all in the console view suits me better. 
 
To do a New York style with the master outs, I'd have to mix both in and out of AD2, so the masters had a mix to work with. That's too fiddly for me.

Do you use AD2's bus output at all?

2:43AM
If the instrument can do all the mixing, then why not just use that to accomplish the same task as outputting all 18 channels separately, mixing, compressing, etc. and then busing them back into common buses again?  I suppose this could give more flexibility, but I think AD2 works well by itself.  All the presets seem to not have the same gel when I mix with separate tracks.  AD2 has its own sound, and I think the master output sounds great.  To me, the easier the better to accomplish the same task.  I am merely a hobbyist, however.

There are advantages to both methods. If you have a workflow, effects and automation etc, that you are used to in Sonar for live drums, output to several tracks makes sense. If your looking for convenience and are okay with the AD2 offerings for effects etc. it makes sense to mix inside the VSTi.
 
Rocky