Those are two different things: 1. Closing Neltharion and 2. Making optional transfers to MoP.
The second one is a good idea. The first one is a horrible idea. If you want Neltharion to disappear for you, there's a simple solution: STOP PLAYING IT. I promise you no one will try to change your mind.
If things end up at a point where there's just a few hundred players who are die hard Neltharion players and want to stay, then let them do so. It's their home. It's not your home if you want to destroy it.
That aside, it's bad business for Warmane to close an expac because it sets a precedent where guys at the next least-popular server start to wonder how long they have, stop playing, stop donating, etc.