If the frame rails are bent in the front (and it sounds like the probably are if the inner fenders have that much damage) then it probably isn't worth fixing, but you could definitely make it happen with a front clip.
If the floorpans BEHIND the frame rails are bent, I think you're done. The likelyhood of the car ever being straight again if the body structure is damaged is about zilch. Easiest way to check for body structure damage is the doors. If the gaps are decent and the doors still line up and open and close, the body is probably ok, or close enough to it to make it work. If the doors are jammed shut or don't line up, the body is bent. Not saying you CAN'T fix it, but more than likely it won't ever be "right" again, and for the time/money/effort you'd be better off buying a new Duster.
Structurally sound Duster bodies are not that much money. Finding one may take a little patience, but I'd probably just take all the useable parts off the one you have and pick up another, that way you don't even have to pay for a car with a drivetrain.