If somebody leaves a void (US?) then the next strongest force (Iran?) will try to fill it.
In the case of Iraq (maybe similar for Syria?) I guess that there aren't probably big motivations/interests nor strong cultural similarities for the West to create something similar to a "Marshall Plan" ( https://en.wikipedia.org/wiki/Marshall_Plan ) to kickstart again the nation and then make it work long-term from both an economic and indirectly social perspective. Therefore, I think that Iraq will just drift more and more towards what will look like the next-best offer(s) (Iran?).
In the case of Iraq (maybe similar for Syria?) I guess that there aren't probably big motivations/interests nor strong cultural similarities for the West to create something similar to a "Marshall Plan" ( https://en.wikipedia.org/wiki/Marshall_Plan ) to kickstart again the nation and then make it work long-term from both an economic and indirectly social perspective. Therefore, I think that Iraq will just drift more and more towards what will look like the next-best offer(s) (Iran?).