this is abandoned fort: http://www.cardgamedb.com/forums/uploads/1283868756/med_gallery_1_64_151278.jpg

lets say I have abandoned fort in play and for whatever reason I want to return one of my own bolton guy to my hand. I initiate a green challenge, let's say with one bolton refugee ( http://www.cardgamedb.com/forums/uploads/1281902045/med_gallery_24_208756.jpg ) and the defending player declares zero defenders.

obviously what I'd want to do is win the challenge and return my guy to my hand after winner determination. is my bolton considered to be an attacker even after winner determination and do I have an opportunity to trigger abandoned fort at that moment?

No. The timing structure doesn't allow it.

Abandoned Fort is a standard "Challenge" phase action. You have to use it during the Player Action Windows of the Challenge phase. The only times that there will be attacking characters during stantand player action windows during the Challenge phase are:

1. Between the "initiate challenge" and "declare defenders" framework windows
2. Between the "declare defenders" and "resolve challenge" framework windows

Once the challenge starts resolving, your next opportunity to use any standard "Challenge" phase action is after the challenge is completely resolved - which means the characters involved are no longer participating in the challenge that just resolved.

In your scenario, you can either return the character to hand, or you can resolve the challenge, but not both.