I honestly wouldn't be shocked if he ends up a Ranger after he hits the free agent market. The Rangers have old fossils(Sosa, Lofton, Cattlanotto) and younger guys who can't get it done(Wilkerson, Cruz, Hairston)
They currently need some power and it is obvious that Texiera won't be hanging around. I am sure Adam would like to go back to Texas and the Astros aren't a fit and Dunn was made for the ballpark in Arlington.
I really have a hard time seeing any scenario where he remains a Red past 2008.