If I'm playing Geo-Force with Madame Xanadu while using her Fortune Telling power, if Geo-Force misses with the attack roll would I then immediately get my Earthen Fist back?

EARTHSHOCK: Geo-Force begins the game with the Earthern Fist attached. Give Geo-Force a power action and place the Earthern Fist in an unoccupied square of clear terrain that is within 10 squares, line of fire, and is adjacent to an opposing character; make a close combat attack targeting the adjacent opposing character. If you hit, the opposing character can't target characters friendly to Geo-Force until the Earthern Fist has been destroyed. The Earthen Fist is considered a square of blocking terrain. When Geo-Force has no action tokens, you may attach the Earthern Fist to Geo-Force.

FORTUNE TELLING: Give Madame Xanadu a power action and choose an adjacent character. When that character misses with an attack this turn, after actions resolve you may remove one action token from that character.

Looks like it would work.

Yup. And it's not even a free action. It just happens. The popular combo for this and other cheese with Geo-Force is Edward Nigma. You attack, hit, use Nigma to remove the action token, and return the fist to your hand to basically lock that character out of combat forever or at least until his friends kill Geo Force or you use the fist later and it gets destroyed (if this was maybe ruled otherwise, I have not seen it yet).