There is a theory that they can reintroduce themselves,but again this is just a theory. There is no evidence that that will or how long it would take.
People kill wolves mainly out of fear.
It is my sincere opinion that our reintroduction efforts are another one of our quick, short term fixes, for a problem that we have created by our own actions. I feel strongly that wolves are very resilient creatures and have overcome great adversities, and that is the reason that they are coming back into states like Wisconsin, Michigan, Idaho, and possibly now Maine. The problems with reintroduction arise with the sudden impact of not only the physical reintroduction, but also the sudden political and societal impacts that arise from the realization that the once and still hated wolf will once again be roaming the hills and forests that we treasure. The impact can be seen already with the shooting of one of the Yellowstone wolves. The animals were moved in too quickly, and people got their undies in a bundle because the change happened too rapidly.