Did you try looking at WotLK FAQ? If this issue isn't in there we should probably post it with all the questions on this.
1) 51 talent respeccing to a variation of the 51 build:
There is nothing you need to worry about. When you unlearn your talents, if your pet is active it will disappear (kinda like when you get out of range). When you respec into the 51 talent, you can resummon him whenever you would like. No worries
2) 51 talent respeccing to non-51
I have not had my exotic active when I do this. I know you don't have to worry, but the 6 week camp on Loq made me decide to stable him for a non-exotic before I respecced. This is what I would advise- heck the stablemaster is right by any hunter trainer anyway. You will continue to have the exotic stabled, and you can't actually get rid of him until you respec into the 51 talent again and take him out. Still, no need to worry about loosing him.
Have fun with your respec, and good luck!
EDIT: DOH! got beat to the reply
Edited, Feb 5th 2009 12:44pm by browningguns