1) Yes, that is exactly my opinion. I think she was preparing to flee and had already set up her base of operations elsewhere. The only way to actually be sure of her presence would be to know if she was there or if her pretty trophies were. All we saw were workers. I think she was already in an alternate base with her most valuable trophies with her. Furthermore, I don't think that she planned to remain in Arad Doman in the first place. She accomplished everything she wanted to, and at this point in the endgame, she had no real purpose there. Heck, she doesn't even like the weather. And I think you miss the point - Moridin's orders to Graendal had changed; Arad Doman had already been broken beyond repair. Graendal was given new orders at the tea party earlier in TGS that no longer required her to stay there (I'd also like to point out that it seems that Aran'gar and Mesaana were given new orders, as well - Aran'gar can no longer stay with the Aes Sedai so Mesaana took over).

2) There is no obvious use for Asan'gar anymore, and s/he is still around. We don't even know if Aginor was brought back. Basically, none of us know the plotline for the next two books so I think it is jumping the gun to try and decide which characters are worthwhile in the long run, and which are not. There are characters in the story that have been around since earlier books that have no "obvious" use anymore, and they are now being referenced as part of other storylines. The point being, I see more use for Graendal than Aran'gar or Mesaana. Moridin's own actions reveal that Graendal's assignment is more longterm than "mess up Arad Doman and then fight al'Thor". Whether a character has any further purpose will be revealed in the fullness of time and over the next books in the series.